American Bison - IUCN Portals

American Bison Status Survey and Conservation Guidelines 2010 Edited by C. Cormack Gates, Curtis H. Freese, Peter J.P. Gogan, and Mandy Kotzman

IUCn/ssC american Bison specialist Group

American Bison Status Survey and Conservation Guidelines 2010 Edited by C. Cormack Gates, Curtis H. Freese, Peter J.P. Gogan, and Mandy Kotzman

The designation of geographical entities in this report, and the presentation of the material, do not imply the expression of any opinion whatsoever on the part of IUCN concerning the legal status of any country, territory, or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries. The views expressed in this publication do not necessarily reflect those of IUCN.

Published by:

IUCN, Gland, Switzerland

Copyright:

© 2010 International Union for Conservation of Nature and Natural Resources Reproduction of this publication for educational or other non-commercial purposes is authorized without prior written permission from the copyright holder provided the source is fully acknowledged. Reproduction of this publication for resale or other commercial purposes is prohibited without prior written permission of the copyright holder.

iv

Citation:

Gates, C.C., Freese, C.H., Gogan, P.J.P. and Kotzman, M. (eds. and comps.) (2010). American Bison: Status Survey and Conservation Guidelines 2010. Gland, Switzerland: IUCN. Revised June 2011.

ISBN:

978-2-8317-1149-2

Cover design by:

C. Cormack Gates

Front cover photo:

Plains bison bull tending a cow (photo Diane Hargreaves/Hargreavesphoto.com)

Back cover photo:

Wood bison cow with calf (photo Doug Lindstrand)

Layout by:

Amy Kelley

Produced by:

IUCN-SSC-American Bison Specialist Group

Printed by:

Insty Prints, Bozeman, Montana

Available from:

The websites of IUCN Publications Services, IUCN/Species Survival Commission, World Wildlife Fund, American Bison Society, and Wildlife Conservation Society

American Bison: Status Survey and Conservation Guidelines 2010

Table of Contents Acknowledgements��xi Authors, contributors and their affiliations��xii Acronyms�� xiii Executive Summary�� xv Chapter 1 Introduction: The Context�� 1 1.1 The Species Survival Commission and the American Bison Specialist Group �� 1 1.2

Context �� 1

1.3

Current Challenges for Conservation and Ecological Restoration of Bison as Wildlife�� 2

1.4

Large Wild Populations�� 2

1.5

Conserving the Wild Character and Genome of Bison�� 3

1.6 Reportable Diseases�� 4 1.7 Purpose of this Document�� 4 Chapter 2 History of Bison in North America�� 5 2.1 Palaeobiology and Phylogeny �� 5 2.2

Original Range�� 6

2.3

Abundance�� 7

2.4

Extirpation�� 8

2.5

Early Recovery�� 8

2.6

Cultural Significance�� 9

Chapter 3 Taxonomy and Nomenclature��13 3.1

An Historical Misnomer: Bison vs. Buffalo��13

3.2

Genus: Bos vs. Bison��13

3.3

Subspecies ��15

Chapter 4 Genetics��19 4.1 Reduction of Genetic Diversity��19 4.2 Hybridisation��21 4.2.1 Plains bison x wood bison��21 4.2.2 Domestic cattle x bison��22 4.3

Domestication��24

Chapter 5 Reportable or Notifiable Diseases ��27 5.1

Diseases of Conservation Concern��28 5.1.1 Anaplasmosis��28 5.1.2 Anthrax��28 5.1.3 Bluetongue��29 American Bison: Status Survey and Conservation Guidelines 2010

5.1.4 Bovine spongiform encephalopathy��30 5.1.5 Bovine brucellosis��30 5.1.6 Bovine tuberculosis��31 5.1.7 Bovine viral diarrhoea��31 5.1.8 Johne’s disease��32 5.1.9 Malignant catarrhal fever (sheep associated)��32 5.2

Episodes of Reportable Diseases in Plains Bison��33 5.2.1 Yellowstone National Park��33 5.2.2 Grand Teton National Park/National Elk Refuge (Jackson herd)��34

5.3

An Occurrence of Reportable Diseases in Wood Bison��35

5.4

Disease Management in Perspective��36

Chapter 6 General Biology, Ecology and Demographics��39 6.1

General Biology��39 6.1.1 Physiology��39 6.1.1.1

Metabolism��39

6.1.1.2

Growth��39

6.1.2 Behaviour��40 6.1.2.1

Social structure ��40

6.1.2.2 Reproductive behaviour��40 6.1.2.3

Cow-calf behaviour��40

6.1.2.4 Horning and wallowing��41 6.1.2.5 6.2

Movements��41

Ecology��42 6.2.1 Plains bison��42 6.2.1.1

Ecological role��42

6.2.1.2

Contemporary habitat use, nutrition, and foraging��43

6.2.1.2.1 Northern mixed grasslands��45 6.2.1.2.2 Central shortgrass prairie��45 6.2.1.2.3 Tall grasslands prairie and southern shortgrass prairie ��45 6.2.1.2.4 Northern fescue grasslands ��45 6.2.1.2.5 Rocky Mountain forest��45 6.2.1.2.6 Northern forests��46 6.2.1.2.7 Arctic lowland taiga��46 6.2.1.3 Habitat and dietary overlap��46 6.2.2 Wood bison��46 6.2.2.1

Original distribution and ecoregions occupied��46

6.2.2.2

Contemporary habitat relationships, nutrition, and foraging��47

6.2.2.2.1 Northern forests��47 6.2.2.2.2 Subarctic boreal forests ��47 6.2.2.3 Habitat and dietary overlap ��47 vi


6.3

Demographics��47 6.3.1 Population structure ��48 6.3.2 Reproduction��49 6.3.3 Mortality factors and survival ��49 6.3.4 Population growth rates ��53

Chapter 7 Numerical and Geographic Status��55 7.1

Introduction��55

7.2

Numerical Status ��56

7.3

Geographic Status��57

7.4 Population Size Distribution��59 7.5

Mate Competition ��60

7.6 Presence of Wolves��60 7.7 Presence of Reportable Diseases��60 7.8

Cattle Gene Introgression��61

7.9

Conclusions��61

Chapter 8 Legal Status, Policy Issues and Listings��63 8.1

Introduction��63

8.2 History of Protection and Conservation

��63

8.2.1 Early legal and policy efforts by governments to protect plains and wood bison�� 63 8.2.1.1

Early policy development in the United States��63

8.2.1.2

Early policy development in Canada��63

8.2.1.3 Policy development in Mexico��64 8.2.2 Plains bison conservation by the private sector ��64 8.2.3 Conservation efforts by tribes and First Nations��64 8.3

Important Policy and Regulatory Considerations ��65 8.3.1 Legal status and listings of bison��65 8.3.1.1

International and global status��65

8.3.1.2

Status in North America��65

8.3.2 Disease status ��73 8.4

Legal and Policy Obstacles Hindering Conservation of Bison��75 8.4.1.1.1 Confusing legal classification and status��75 8.4.1.1.2 Historical management policies��75 8.4.1.1.3 Complex partnerships needed to manage large landscapes��75 8.4.1.1.4 Defining the social and economic value of wild bison��76 8.4.1.1.5 Coordination of policies, rules, and regulations by government��76 8.4.1.1.6 Agricultural conflicts among mixed land ownership��76

8.5

Overcoming Obstacles to the Ecological Restoration of Bison��77 8.5.1 Disease management considerations��77 8.5.2 Legal status and policy considerations��77 American Bison: Status Survey and Conservation Guidelines 2010 vii

8.5.2.1 Role of the non-governmental organisations��77 8.5.2.2

State/provincial and federal governance��78

8.5.2.3 The private sector��78 8.5.2.4

Indigenous peoples��78

8.5.2.5

Local communities and economies��79

8.5.3 Coordination of agency missions, goals, regulations, and policies affecting bison conservation and restoration��80 8.5.4 Recommendations��80 8.5.5 Recent initiatives to conserve and restore bison��81 8.5.5.1

United States��81

8.5.5.2

Canada��82

8.5.5.3

Mexico��83

8.5.5.4

Non-governmental organisations��83

8.5.5.5 Tribal initiatives��84 Chapter 9 Conservation Guidelines for Population, Genetic, and Disease Management��85 9.1

Introduction and Principles��85

9.2

Guidelines for Population and Genetic Management��86 9.2.1 Guidelines that apply to most conservation herds��87 9.2.2 Herd-level population and genetic management��88 9.2.2.1

Soft release procedures��88

9.2.3 Establishing a new herd��88 9.2.4 Maintaining or manipulating existing herd size��89 9.2.5 Transferring bison between herds��90 9.2.6 Recovering small or threatened herds��91 9.2.7 Recovering herds from germplasm introgression ��92 9.2.8 Herd size reduction��92 9.3

Behaviour: Mating System, Social Structure, and Movements��92 9.3.1 Social structure and spacing��93 9.3.2 Foraging and movements��93 9.3.3 Mating behaviour��94 9.3.4 Limiting factors and natural selection��94

9.4 Habitat and Biodiversity Management ��94 9.5

Disease Guidelines: Considerations for Infected and Uninfected Herds ��95 9.5.1 Prevention��96 9.5.2 Surveillance��96 9.5.3 Management��97 9.5.4 Research��97 9.5.5 Stakeholder involvement��97

viii


9.6

Active Management: Handling, Herding, Infrastructure��98 9.6.1 Handling��98 9.6.2 Fencing��99 9.6.3 Corrals, pens, and chutes��99

9.7

Modelling to Assess Bison Populations and Habitat �� 100 9.7.1 Guidelines for using computer simulations �� 100

9.8

Conclusions�� 101

Chapter 10 Guidelines for Ecological Restoration of Bison�� 103 10.1

Introduction�� 103

10.2

Ecological Restoration�� 104 10.2.1

Geographic potential for ecological restoration�� 104

10.2.2 P rinciples for ecological restoration applicable to bison�� 105 10.3 The “Ecosystem Approach” for Designing Ecological Restoration of Bison�� 107

10.4

10.3.1

Defining the biological landscape and objectives�� 107

10.3.2

Defining the social landscape, the main stakeholders, and cultivating partnerships �� 107

Guidelines for Planning and Implementing Ecological Restoration Projects for Bison�� 109 10.4.1.1 Feasibility assessment�� 109 10.4.1.2 Suitable release stock�� 110 10.4.1.3 Preparation and release�� 110 10.4.1.4 Socio-economic and legal requirements�� 111 10.4.1.5 Monitoring, evaluation, and adaptation�� 111

10.5

Summary�� 112

Literature Cited�� 113 Appendix A North American conservation herds of bison and their managing authorities�� 131

American Bison: Status Survey and Conservation Guidelines 2010 ix


Acknowledgements This manuscript is the product of more than three years of cooperative effort by numerous contributors, many of whom are listed as authors. Their knowledge and particularly their persistence were instrumental in seeing this major undertaking through to successful completion. The editors express their appreciation to Joe Truett with the Turner Endangered Species Fund for his advice on compiling this document. We acknowledge the support of institutions and organisations that authorised members of the Bison Specialist Group and others to contribute to the project. They include the following in no particular order of priority: U.S. National Park Service; U.S. Fish and Wildlife Service; U.S. Geological Survey Biological Resources Division; Parks Canada Agency; Canadian Wildlife Service; Department of National Defense in Canada; Comisión Nacional de Areas Naturales Protegidas, Mexico; Universidad Nacional Autónoma de México, Instituto de Ecología; State of Montana Fish, Wildlife and Parks; South Dakota Game Fish and Parks; Alaska Department of Fish and Game; Yukon Department of the Environment; Northwest Territories Environment and Natural Resources; Northern Great Plains Office of the World Wildlife Fund; Wildlife Conservation Society; The American Bison Society; The Nature Conservancy; Turner Endangered Species Fund; Turner Enterprises; Inter-Tribal Bison Cooperative; Council of Athabascan Tribal Governments; Faculty of Environmental Design, and the Department of Archaeology in the Faculty

of Social Sciences at the University of Calgary; College of Veterinary Medicine and Biomedical Sciences, Texas A&M University; Department of Anthropology, University of Alaska, Fairbanks; Department of Zoology, University of Oklahoma; the Canadian Bison Association; and the National Bison Association. We also wish to acknowledge logistical support provided by Vermejo Park Ranch, and particularly the generosity of Marv Jensen and Ted Turner, who co-hosted a meeting of the Bison Specialist Group in 2005 to organize the writing project. The Wildlife Conservation Society subsequently hosted two meetings to develop a vision for bison restoration in North America in which many members of the American Bison Specialist Group participated. These workshops were instrumental in building working relationships, sharing knowledge, and developing a sense of mission, which contributed to the project’s success. The U.S. Geological Survey and Wildlife Conservation Society provided support for technical editing, formatting and compilation of the document. Finally, the World Wildlife Fund Northern Great Plains Program—particularly staff members Steve Forrest and Peder Groseth—was instrumental in developing a framework for bison conservation, adding content and guiding the production of this document by providing financial and technical support for the first Vermejo meeting and subsequent meetings and for technical editing, layout, and publication of the final document.

American Bison: Status Survey and Conservation Guidelines 2010 xi

Authors, contributors and their affiliations Aune, Keith

Wildlife Conservation Society, Bozeman, Montana, USA

Berger. Joel


Boyd, Delaney P.

Department of National Defence, Canadian Forces Base Suffield, Medicine Hat, Alberta, Canada

Derr, James N.

Department of Veterinary Pathobiology, Texas A&M University, College Station, Texas, USA

Elkin, Brett T.

Government of the Northwest Territories, Department of Environment and Natural Resources, Yellowknife, Northwest Territories, Canada

Ellison, Kevin


Freese, Curtis H.

Bozeman, Montana, USA

Gates, C. Cormack

Faculty of Environmental Design, University of Calgary, Calgary, Canada

Gerlach, S. Craig

Department of Cross-Cultural Studies and Resilience and Adaptation Program, University of Fairbanks, Alaska, USA

Gogan, Peter J.P.

United States Geological Survey, Northern Rocky Mountain Science Center, Bozeman, Montana, USA

Gross, John E.

U.S. National Park Service, Fort Collins, Colorado, USA

Halbert, Natalie D.

Department of Veterinary Pathobiology, Texas A&M University, College Station, Texas, USA

Hugh-Jones, Martin

Department of Environmental Sciences, School of the Coast and Environment, Louisiana State University, Baton Rouge, Louisiana, USA

Hunter, David

Turner Endangered Species Fund, Bozeman, Montana, USA

Joly, Damien O.

Wildlife Conservation Society, Nanaimo, British Columbia, Canada

Kotzman, Mandy

Creative Pursuits LLC, La Port, Colorado, USA

Kunkel, Kyran

World Wildlife Fund, Bozeman, Montana, USA

Lammers, Duane J.

Rapid City, South Dakota, USA

Larter, Nicholas C.

Department of Environment and Natural Resources, Government of the Northwest Territories, Fort Simpson, Canada

Licht, Daniel

U.S. National Park Service, Rapid City, South Dakota, USA

List, Rurik

Instituto de Ecología, Universidad Nacional Autónoma de México, Mexico City, Mexico

Nishi, John

ALCES Group, Calgary, Alberta, Canada

Oetelaar, Gerald A

Department of Archaeology, University of Calgary, Calgary, Alberta, Canada

Paulson, Robert L.

The Nature Conservancy, Rapid City, South Dakota, USA

Potter, Ben A.

Department of Anthropology, University of Alaska, Fairbanks, USA

Powers, Jenny


Shaw, James H.

Natural Resource Ecology and Management, Oklahoma State University, Stillwater, Oklahoma, USA

Stephenson, Robert O.

Alaska Department of Fish and Game, Fairbanks, Alaska, USA

Truett, Joe

Turner Endangered Species Fund, Glenwood, New Mexico, USA

Wallen, Rick

U.S. National Park Service, Yellowstone National Park, Mammoth, Wyoming, USA

Wild, Margaret


Wilson, Gregory A.

Canadian Wildlife Service, Edmonton, Alberta, Canada

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Acronyms ABS

American Bison Society

CSP

Custer State Park, South Dakota

ABSG

American Bison Specialist Group, a division of the IUCN BSG

CWS

Canadian Wildlife Service

CWCS

Comprehensive Wildlife Conservation Strategy

ADFG

Alaska Department of Fish and Game

DNDC

The Department of National Defence, Canada

AGFD

Arizona Game and Fish Department

EHD

Epizootic hemorrhagic disease

ALCES®

A Landscape Cumulative Effects Simulator, FOREM Technologies

EINP

Elk Island National Park, Alberta

ANPP

Herbaceous above ground net primary productivity

EIS

Environmental Impact Statement

ESA

U.S. Endangered Species Act

APF

American Prairie Foundation

ESU

Evolutionarily significant unit

APFRAN

Animal Plant and Food Risk Assessment Network, Canada

FAD

Foreign Animal Disease

FEARP

U.S. Department of Agriculture Animal and Plant Health Inspection Service

Federal Environmental Assessment Review Panel, Canada

FMD

Foot-and-mouth disease, or heartwater

BLU

Bluetongue

FNNWR

BNP

Badlands National Park, South Dakota

Fort Niobrara National Wildlife Refuge, Nebraska

BRCP

Bison Research and Containment Program, Northwest Territories

GEU

Geminate evolutionary unit

GTNP

Grand Teton National Park, Wyoming

BSE

Bovine spongiform encephalopathy

GWBE

Greater Wood Buffalo Ecosystem, Canada

BSG

IUCN Bison Specialist Group

GWBNP

Greater Wood Buffalo National Park, Canada

BTB

Bovine tuberculosis

GYA

Greater Yellowstone Area

BVD

Bovine viral diarrhoea

HMSP

Henry Mountains State Park, Utah

CAMP

Conservation Action Management Plan process, IUCN Captive Breeding Specialist Group

HOAA

Health of Animals Act, Canada

InVEST

Integrated Valuation of Ecosystem Services and Tradeoffs

ITBC

Intertribal Bison Cooperative

IUCN SSC

IUCN Species Survival Commission

IUCN SUSG

IUCN Sustainable Use Specialist Group

JD

Johne’s disease

APHIS

CATG

Council of Athabascan Tribal Governments, Alaska

CBA

Canadian Bison Association

CBD

International Convention on Biological Diversity

CBSG

IUCN/SSC Conservation Breeding Specialist Group

MBS

Mackenzie Bison Sanctuary, Northwest Territories

CDOJ

Canadian Department of Justice

MCA

Montana Code Annotated

CFIA

Canadian Food Inspection Agency

MCF

Malignant catarrhal fever

CITES

Convention on International Trade in Endangered Species of Wild Fauna and Flora

MDOL

State of Montana Department of Livestock

MFWP

State of Montana Department of Fish, Wildlife and Parks

CMN

Canadian Museum of Nature

CONANP

Comision Nacional De Areas Naturales Protegidas, Mexico

MLVA

Multiple locus, variable number, tandem repeat analysis

COSEWIC

Committee on the Status of Endangered Wildlife in Canada

MtDNA

Mitochondrial deoxyribonucleic acid

N

Population size

American Bison: Status Survey and Conservation Guidelines 2010 xiii

NBA

National Bison Association, U.S.A

SERI

Society for Ecological Restoration International

NBMB

Northern Buffalo Management Board, Canada

SERS

Society for Ecological Restoration Science

NBR

National Bison Range, Montana

SHNGP

NCC

Nature Conservancy of Canada

Sully’s Hill National Game Preserve, North Dakota

Ne

Effective population size

SRL

NEP

Nonessential experimental population

Slave River Lowlands, Northwest Territories, Canada

NEPA

National Environmental Policy Act, U.S.A

SNMNH

Smithsonian National Museum of Natural History

NER

National Elk Refuge, Wyoming

SWAP

NGO

Non-governmental organisation

State Wildlife Action Plan (name varies by state)

NPS

U.S. National Park Service

TB

Tuberculosis

NRCS

Natural Resource Conservation Service, U.S.A

TGPP

Tallgrass Prairie Preserve, Oklahoma

NWT

Northwest Territories, Canada

TNC

The Nature Conservancy

NTENR

Northwest Territories Environment and Natural Resources

TRNP

Theodore Roosevelt National Park, North Dakota

OIE

World Organization for Animal Health

TSE

Transmissible spongiform encephalopathies

PANP

Prince Albert National Park, Saskatchewan

TESF

Turner Endangered Species Fund

PCA

Parks Canada Agency

USNARA

PES

Pay-for-Environmental Services

U.S. National Archives and Records Administration

PHVA

Population and Habitat Viability Assessment

USDA

U.S. Department of Agriculture

PPAs

Private protected areas

USDOI

U.S. Department of the Interior

PVA

Population viability analysis

USFS

U.S. Forest Service

RAC

Research Advisory Committee for bison disease research in WBNP

USFWS

U.S. Fish and Wildlife Service

USGSBRD

U.S. Geological Survey Biological Resources Division

VJDHSP

Voluntary Johne’s Disease Herd Status Programme (for cattle)

WBNP

Wood Buffalo National Park, Alberta and Northwest Territories

WBP

Wainwright Buffalo Park, Alberta

WCNP

Wind Cave National Park, South Dakota

WCS

Wildlife Conservation Society

WHO

World Health Organization

WMNWR

Wichita Mountains National Wildlife Refuge, Oklahoma

RDR

Reportable Diseases Regulations

ˆr

Observed exponential rate of population increase

rm

Maximum exponential rate of population increase

RMEF

Rocky Mountain Elk Foundation

SAGARPA

Secretary of Agriculture, Livestock Production, Rural Development, Fishery and Food, Mexico

SCBD

Secretariat of the Convention on Biological Diversity

SDGFP

South Dakota Game, Fish and Parks

SEMARNAT

Secretaría de Medio Ambiente y Recursos Naturales, México

WWF

World Wildlife Fund

YDOE

Yukon Department of the Environment

SENASICA

Servicio Nacional de Sanidad, Inocuidad y Calidad Agroalimentaria, Mexico

YNP

Yellowstone National Park, Idaho, Montana and Wyoming

YT

Yukon Territory, Canada

xiv


Executive Summary Curtis H. Freese and C. Cormack Gates

The publication of this IUCN American Bison Status Survey and Conservation Guidelines is timely owing to a recent convergence of factors: new research findings on bison genetics and ecology, assessment and awareness of the precarious status of many bison conservation herds, new initiatives by government and non-profit institutions to improve management of existing herds and to establish conservation herds, growing interest among Native Americans in restoring bison as part of their cultural heritage, and an increasing awareness by the commercial bison industry that conservation of wild-type bison is in the longterm interest of the industry. There is also a growing body of evidence that the biodiversity of ecosystems within the original range of bison can benefit from bison restoration, from the desert grasslands of northern Mexico, through the Great Plains, to the lowland meadow systems of interior Alaska. The ten chapters of this book examine these and other aspects of the biology and conservation of the species, and offer guidelines for what we anticipate will be a new era of bison conservation in North America. Under the auspices of the IUCN American Bison Specialist Group, twenty-nine chapter coordinators and contributors share their knowledge and ideas in this comprehensive review of the diverse topics that need to be considered by researchers, managers, policy makers and others interested in restoring and conserving this magnificent animal. In the introductory chapter, C. Gates and P. Gogan explain the overall purpose of the IUCN American Bison Specialist Group and this document. The Specialist Group is composed of more than 60 registered members and numerous collaborators from the three nations comprising North America and ranging from Chihuahua State in Mexico to the State of Alaska. The Group operates under the aegis of the IUCN Species Survival Commission. The authors note that the purpose of this volume is to contribute to the development of strategies and actions that, where feasible, will conserve and ecologically restore bison as wildlife throughout their original range. Gates and Gogan acknowledge that large-scale restoration of bison is an ambitious and complex undertaking, perhaps unparalleled in species conservation efforts in North America. Their introduction briefly reviews the major issues facing bison conservation and the strong influence that bison historically exerted on ecosystems across much of the continent. Apart from the ecological importance of bison, the social and cultural significance of bison restoration is recognised when they state, “no other wildlife species has exercised such a profound influence on the human history of a continent.”

In Chapter 2, B. Potter and co-authors trace the evolutionary and recent history of bison, beginning with the earliest fossil records showing bison in Asia at least two million years ago, and continuing with their expansion, much later, into North America across the Bering Land Bridge during the middle Pleistocene. The evolution and distribution of various bison species and subspecies in North America present a complex story shaped, in large part, by bison habitat and ranges that shifted widely with advancing and retreating continental ice sheets. The result of this evolutionary history today is two species, the European bison and American bison, and two subspecies of American bison, wood bison and plains bison. Five hundred years ago, tens of millions of plains bison probably inhabited North America, from southern Canada to northern Mexico, and from nearly the west coast to the east coast, with the Great Plains as their centre of abundance. Wood bison, because of a more restricted boreal forest habitat, were much less numerous. For many native peoples of North America, thousands of years of coexistence had led to bison being central to their survival and cultures, a history that Potter et al. explore in some detail. European colonisation of North America brought rapid change to both bison and Native Americans. Commercial hunting, competition with livestock, killing of bison as government policy to subjugate Indian tribes, and other causes led to the precipitous decline of both plains and wood bison. By the end of the 19th Century a few hundred bison survived in various small captive and wild herds across North America. Fortunately, conservation efforts quickly emerged in both Canada and the United States (U.S.) and, once protected, bison numbers began to recover. Their iconic status now seems to be recovering also. Potter et al. echo what other authors of this volume have expressed when they note that no other North American species holds such great cultural and political significance. In Chapter 3, D. Boyd and co-authors review the confusing and disputed evidence for, and diverse opinions about, bison taxonomy. Agreement seems to end with the consensus that bison belong to the family Bovidae. Much of the debate centres on whether bison belong to the genus Bos, the genus of cattle, guar, yak, and oxen, or to their own genus, Bison. Both names are currently used in the scientific literature. Differences of opinion are largely based on the importance of morphological (phenetic) versus molecular (phylogenetic) lines of evidence, and on historical precedence and usage. Within Bison, there are also some people who question the designation of European bison and American bison as separate species. Boyd et al. conclude

American Bison: Status Survey and Conservation Guidelines 2010 xv

that “Further research and debate by taxonomists, and the bison conservation community, is required to reconcile molecular, behavioural and morphological evidence before a change in nomenclature could be supported, and thus, for this document, the American Bison Specialist Group adheres to the genus Bison with two species, B. bonasus and B. bison. Not surprisingly, disagreement also exists regarding the subspecies status of wood and plains bison. However, Boyd et al. emphasise that this debate does not negate the importance of conserving the two forms as separate entities. From a conservation perspective, the goal is to conserve “evolutionarily significant units” or “distinct population segments,” among other terms used to define geographic variation among populations, a concept recognised by both the U.S. Endangered Species Act and the Committee on the Status of Endangered Wildlife in Canada. Keeping wood bison and plains bison as separate non-interbreeding units is the recommended precaution. Genetics play a particularly complex and important role in bison conservation, as explained by D. Boyd and co-authors in Chapter 4. The rapidly advancing science of genetics has recently brought new information and insights into not just the evolutionary relationships among bison taxa, but also to managing for viable bison populations and conserving the wild bison genome. Boyd et al. review the current state of bison genetics and what needs to be done to address the major threats to genetic diversity and integrity—demographic bottlenecks, founder effects, genetic drift, and inbreeding—all of which bison have experienced. Although population bottlenecks can lead to significant loss of genetic diversity, bison appear to have largely avoided this problem during their population bottleneck in the late 1800s. Given the good diversity within the bison gene pool, and recent evidence that shows several conservation herds are genetically distinguishable, one of the most important management questions is how to manage the population genetics of these often relatively small herds. Should this be accomplished as one large metapopulation or as closed herds to maintain localised diversity? The best conservation strategy is to do both, and, where possible, to increase the size of small herds to attain a large effective population size. Hybridisation also poses challenges for bison conservation. Although the introduction of plains bison into wood bison range has resulted in some hybridisation, the two forms remain distinct and avoiding further hybridisation is a priority. Much more widespread, and of greater concern, is the introgression of cattle genes into the bison genome, a legacy of attempts to crossbreed cattle and bison that began when bison numbers were still low in the early 1900s. Genetic testing reviewed by Boyd et al. indicates that most conservation herds have some level of cattle-gene introgression in the nuclear and (or) mitochondrial DNA. By inference this strongly suggests that a vast majority of commercial herds have cattle-gene introgression. The effects xvi

of introgression on bison biology are largely unknown. No introgression has been detected in several conservation herds, which consequently deserve priority attention for maintaining in reproductive isolation, and as source stock for establishing new conservation herds. Finally, Boyd et al. note that the approximately 400,000 bison in commercial herds in North America, some 93% of the total continental population, are undergoing artificial selection for domestic traits, such as ease of handling, body conformation, carcass composition, and so on. Domestication, whether intentional or not, poses a special challenge to conserving the wild bison genome. In Chapter 5, K. Aune and co-authors provide a comprehensive review of how diseases, particularly those that are “reportable” according to federal or state/provincial regulations, have a major influence on bison restoration and management. They describe the characteristics and implications of nine diseases for bison conservation, ranging from anthrax and bluetongue to bovine brucellosis and bovine spongiform encephalopathy. Federal and state/provincial regulations for, and management responses to, a particular disease depend on several factors, including potential effects on bison, threat to livestock and humans, and whether it is indigenous or exotic to bison and the ecosystem. The authors describe the complex and difficult management challenges that diseases present in three of North America’s most important conservation herds: the plains bison herds of Yellowstone National Park (YNP) and Grand Teton National Park/National Elk Refuge that harbour brucellosis, and the wood bison herds in and around Wood Buffalo National Park that are infected with both bovine tuberculosis (BTB) and brucellosis. Diseases such as brucellosis also severely limit the translocation of bison from infected, important conservation herds, such as the Yellowstone herd, to establish new herds in new areas because of concerns about potential transmission to cattle. While the policies and legal framework for controlling disease in domestic livestock are well established, they do not work well when applied to wildlife, including bison, because they often conflict with conservation goals and our ability to manage and maintain wild populations. The recent development of national wildlife health strategies in both Canada and the U.S. could help address this problem. Chapter 6, by P. Gogan and co-authors, addresses general biology, ecology, and demographics of bison. Bison are remarkably adaptable to a wide range of ecosystems and climatic regimes. Physiologically, bison are much better adapted to climate extremes than cattle. Behaviourally, bison exhibit a relatively simple social structure with cow-calf pairs at the core and, more loosely and somewhat seasonally, large groups of cows, calves and immature males, and separate, smaller groups of mature bulls. Bison exhibit individual and group defence against large predators such as wolves. Historically, plains bison made seasonal migrations between summer and winter ranges, in some cases north-south and in others between the prairies


and foothills. Bison have a profound influence on ecosystems and create habitat heterogeneity through various means. As primarily graminoid (grasses and sedges) eaters, variable grazing pressure by free-ranging bison and their interaction with fire create habitat patchiness on which grassland bird diversity depends. Wallowing behaviour further promotes heterogeneity by forming temporary pools and changing surface hydrology and runoff and creating local patches of disturbed soil in which some flowering plant species prosper. Bison are dispersers of seeds, and are sources and redistributors of nutrients for predators, scavengers, plants, and ecosystem processes. Gogan et al. describe foraging patterns and habitat use by wood and plains bison in various ecoregions, from the arid southwest to humid cold boreal regions. The authors also review bison population structure and reproduction and demonstrate that under natural conditions newly established bison populations can double every four to six years. Population numbers are affected by both density-independent events, such as severe winters and wild fires, and density-dependent factors such as disease and wolf predation. While humans were a bison predator for thousands of years, the advent of firearms greatly increased human predation, so that by the mid-1800s, an estimated 500,000 plains bison were killed annually for subsistence and 100,000 for hides. The human-firearm-commerce combination, it would seem, largely voided the density-dependent relationship between bison and human predation until it was almost too late for the American bison. In Chapter 7, C. Gates and co-authors assess the status of conservation herds using seven criteria: numerical status, geographic status, population size and class distribution, opportunity for mate competition among mature males, presence of wolves, presence of diseases that could affect conservation status, and occurrence or likely occurrence of cattle-gene introgression. The designation “conservation herd” is assigned to herds managed by federal or state/provincial governments or non-governmental organisations (NGOs) whose mission is nature conservation. Remarkably, little progress has been made in recent decades in increasing the number of animals in conservation herds. From the few hundred that remained in the late 1800s, the number of animals in conservation herds increased in the first half of the 1900s, but then levelled off, or in the case of the wood bison, even declined, while the number of conservation herds has continued to grow to the present day. As of 2008, there were 62 plains bison conservation herds containing about 20,500 animals, and 11 conservation herds of wood bison containing nearly 11,000 animals. Meanwhile, starting in the 1980s, the commercial bison industry prospered with the total population growing to around 400,000 animals in 2007, roughly evenly divided between the U.S. and Canada. Although a few conservation herds exceed 1,000 animals, most conservation herds of both wood and plains bison have fewer

than 400 animals and, in the case of the plains bison, many are fenced in areas of only a few thousands hectares and not subject to natural predation. Until recently, there was a wild bison herd inhabiting a trans-boundary area between Mexico and the U.S., the only herd meriting conservation status in Mexico. But now, it has been restricted to a private ranch on the U.S. side. The American bison nearly qualifies for listing as Vulnerable Ca2(1) under IUCN criteria and is currently listed as Near Threatened on the IUCN Red List. As K. Aune and co-authors describe in Chapter 8, bison conservation must deal with a complex maze of legal and policy issues. Much of this complexity is due to a history of bison being treated like livestock. As the authors note, “During the great restoration period of wildlife management, bison were routinely classified and managed by state/provincial and federal agencies across North America as a form of livestock, while other wildlife were classed and managed as free-roaming wild animals.” They subsequently provide a detailed review of the legal status of, and conservation initiatives underway for, bison in Mexico, the U.S., and Canada. The legal recognition of bison as wildlife or livestock, or both, varies across various federal, state, and provincial jurisdictions in North America. For example, only ten U.S. states, four Canadian provinces and two territories, and one Mexican state classify bison as wildlife; all other states and provinces within the bison’s historic range designate them as domestic livestock. Overlaying this legal map for bison are several stakeholder groups that manage bison: public wildlife and land management agencies, Native American groups, non-profit conservation organisations, and private producers. Reportable diseases present another set of legal issues that affect international and interstate transport of bison. Aune et al. suggest that a paradigm shift is required whereby the public recognises bison as wildlife, and that there is much greater social tolerance, especially in the agricultural community, if major progress is to be made in re-establishing free-ranging bison on their native range. Moreover, large-scale restoration over big landscapes will typically require partnerships and co-management among multiple landowners and resource managers, and more enlightened and coordinated government regulations and policies. In Chapter 9, J.E. Gross and co-authors provide guidelines for population, genetic, and disease management for both existing conservation herds and for the full recovery of bison over both the short and long term. As the authors explain, conservation focuses on retaining existing ecological, cultural, and genetic characteristics of bison, whereas full recovery entails a broader vision of bison inhabiting landscapes that permit the full expression of natural behaviours and ecosystem interactions that once existed. The guidelines first address bison behaviour, particularly the importance of ensuring natural mating systems that involve avoiding a skewed sex ratio and allowing

American Bison: Status Survey and Conservation Guidelines 2010 xvii

competition among bulls, as well as other factors, such as natural movements and mortality rates. Given the small size of many existing herds and newly established herds, guidelines for population and genetic management are particularly important. Herds of 1,000 or more animals are important for conserving genetic diversity, and factors such as non-random mating, skewed sex ratios, and large swings in population size need to be avoided in relatively small herds. Managing bison for restoring and maintaining biodiversity involves allowing animals to naturally move and forage across the landscape, and to interact with other natural processes such as fire, drought, and snow cover. Guidelines are provided for active management, including handling and herding and the type of infrastructure required, with the caveat that active management and handling should be minimised. Disease guidelines address prevention, surveillance and, when pathogens are detected, management. Gross et al. stress the importance of well-designed reintroduction programs for establishing new herds and offer suggestions ranging from stakeholder involvement to sourcing animals and ensuring proper herd structure. Given concerns about the genetic uniqueness of some herds and cattle-gene introgression, similar care needs to be given in transferring animals between herds with the goal of maintaining genetic diversity and (or) aiding in the recovery of small or threatened herds. The chapter concludes with recommendations for using modelling and computer simulations to assess bison populations and habitat.

The concluding chapter (10) on guidelines for ecological restoration by C. Gates and co-authors is directed at establishing new, large populations of bison on large landscapes. Because bison were an ecologically dominant species over much of their range, restoring historic ecological processes and biodiversity in areas they once inhabited depends on restoring large, free-roaming herds. Full ecological restoration is defined as “the re-establishment of a population of several thousand individuals of the appropriate subspecies in an area of original range in which bison interact in ecologically significant ways with the fullest possible set of other native species and biophysical elements of the landscape, with minimal necessary management interventions.” Although the focus of this chapter is on restoring large herds over large areas, where processes such as migration and natural selection are most likely fulfilled, Gates et al. point out that small herds can also contribute to restoring many ecological processes that occur at smaller scales. The chapter provides guidelines for planning and executing large-scale re-introductions, including a feasibility analysis that addresses both biological questions and a thorough assessment of socioeconomic variables and legal requirements, sourcing and then reintroducing suitable stock, and follow-up monitoring, evaluation and adaptation as experience is gained and lessons learned. As noted as well in chapter 8, one of the biggest challenges facing large-scale restoration is that assembling a landscape of hundreds of thousands or millions of hectares will usually require partnerships and co-management of multiple landowners, both public and private, and the support of many stakeholders.

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Chapter 1

Introduction: The Context Lead authors: C. Cormack Gates and Peter J. P. Gogan

1.1 The Species Survival Commission and the American Bison Specialist Group

The ABSG is a group of volunteers representing a variety of disciplinary backgrounds, expertise, and professional experience. They are geographically distributed across the breadth of the original continental range of the species, from Mexico to Alaska, and from the Tallgrass Prairie in the east to the intermountain west. They work for a variety of institutions including governments, conservation organisations, and academic institutions (see Acknowledgements).

The International Union for Conservation of Nature (IUCN) Species Survival Commission (SSC) is a science-based network of approximately 8,000 volunteer experts from almost every country of the world, working together towards “A world that values and conserves present levels of biodiversity.” Within the SSC, over 100 specialist groups and more than 15 independent Red List Authorities are set up to track The primary goal of the American Bison Specialist species’ status, monitor biodiversity, analyse issues, develop solutions, and implement Group (ABSG) is to contribute to the development of actions (SSC Strategic Plan 2001-2010). comprehensive and viable strategies and management Among them, the Bison Specialist Group is actions to enhance conservation and achieve ecological distinguished by two organisational units, one for the European bison (Bison bonasus), restoration of bison as wildlife where feasible throughout and the other, for the American bison (Bison bison). 1.2 Context The primary goals of the American Bison Specialist Group (ABSG), and the intent of this document, are to contribute to the development of comprehensive and viable strategies and management actions to promote conservation and ecological restoration of bison as wildlife where feasible throughout the original range of the species. Conservation and ecological restoration of bison, as wildlife, at the scale of its original continental range are ambitious and complex endeavours, perhaps more so than for any other North American species. Enhancing the long-term security of bison, as wildlife, will require the commitment and participation of key sectors, including public wildlife and land management agencies, non-government environmental organisations, aboriginal governments and communities, local communities, and conservation-oriented commercial producers. Toward this goal, the ABSG was established to include a broad network of people interested in bison conservation and recovery. There are more than 60 registered members and numerous other collaborators. As with other specialist groups, this network of volunteers represents the functional capacity of the IUCN to monitor the status and management of American bison in relation to global and local biodiversity. Specialist Group participants contributed the scientific and practical knowledge assembled in this report, and can offer expert advice and, in many instances, the means to make things happen on the ground by implementing actions or encouraging and facilitating others to advance the conservation and ecological restoration of bison as wildlife.

Prior to European settlement, the American bison had the largest original distribution of any indigenous large herbivore in North America, ranging from the desert grasslands of northern Mexico to the floodplain meadows of interior Alaska (List et al. 2006; Stephenson et al. 2001) and almost from coast to coast. The ecological scope of the species was limited only by its habitat requirements and specialised diet. An obligate grazer, grasses and sedges present in grasslands and meadows are the mainstay of the American bison’s diet and habitat. Bison have been continuously present in North America for at least 300,000 years, persisting in various forms during the late Pleistocene through sequential glacial and interglacial periods, then into the Holocene and present times (MacDonald 1981; Shapiro et al. 2004; Wilson et al. 2008). They have been associated with successive cultures since humans first occupied the continent about 12,000 years ago. Over hundreds of thousands of years, bison have contributed to the co-evolution of other biota, including grazing adaptations in plants, mutualistic, commensal and trophic interrelationships, and bison have functioned as a key component of the native biodiversity in vast areas of the continent. Key species, such as bison, have a marked influence on the patterns of occurrence, distribution, and density of other species (Meffe and Carroll 1994; Paine 1969). Where present, bison play important ecological roles by influencing the structure, composition and stability of both plant (Campbell et al. 1994; Knapp et al. 1999) and animal communities (Bogan 1997; Roe 1970; Truett et al. 2001).


No other wildlife species has exercised such a profound influence on the human history of a continent. As the great ice sheets receded, and grasses and sedges colonised the emerging landscape, beginning 14,000 years ago, bison, then human cultures followed. Widespread and abundant (Shaw 1995), bison were a staple resource for more than 12,000 years in the subsistence economies of successive cultures of Native North Americans. During brief recent history, over the last 500 years or so, Europeans colonised the eastern seaboard, explored westward into the Native-occupied prairies and the North, fought for resources, dominated indigenous peoples, and prospered as new settlers and industrial societies. Trading posts recruited indigenous people to harvest bison for meat and pemmican for the forts and to fuel the trade in furs (Gates et al. 1992). Armies clashed under the prairie skies (Greene 1996) and railways were built to connect the West to eastern markets. Millions of plains bison were killed for their meat, hides for machine belts and robes, for sport, and to subjugate the First Nations, making way for settler society and domestic European livestock (Hornaday 1889; Isenberg 2000). In less than a century, from Chihuahua State in Mexico to the State of Alaska, the most abundant indigenous large herbivore in North America was driven close to extinction. Had it not been for the interest of private citizens in rearing a few survivors in captivity (Coder 1975), and the remoteness of a lone wild population in what is now Yellowstone National Park (YNP) (Meagher 1973), plains bison would have disappeared from the continent. Similarly, by the end of the “Great Contraction” of plains bison late in the 19th Century (Flores 1996), wood bison were also reduced to a single surviving population of fewer than 300 animals in a remote area in the forested borderlands of Alberta (AB) and the Northwest Territories (NWT) (Gates et al. 1992; 2001).

ecological adaptation resulting from natural selection operating on individuals in viable populations in the wild (IUCN 2003; Secretariat of the Convention on Biological Diversity 1992; Soulé 1987). In wild mammal populations, limiting factors, such as predation, seasonal resource limitation, and mate competition, contribute to maintaining the wild character, genetic diversity, and heritable traits that enable a species to adapt to, and persist, in a natural setting (Knowles et al. 1998). The longterm conservation of American bison as wildlife is faced with several important challenges that need to be acknowledged and addressed by public agencies, non-profit organisations and producer organisations. They include the rarity of large wild populations in extensive native landscapes, conserving the wild character and genome of bison, and the presence of regulated diseases.

1.4

Large Wild Populations

Bison can best achieve their full potential as an evolving, ecologically interactive species in large populations occupying extensive native landscapes where human influence is minimal and a full suite of natural limiting factors is present. While such conditions remain available in the north of the continent, it is challenging to find extensive landscapes for restoring and sustaining large free-roaming wild bison populations in southern, agriculture-dominated regions. Ecological restoration is the intentional process of assisting recovery of an ecosystem that has been modified, degraded, damaged or destroyed relative to a reference state or trajectory through time (SERI and IUCN Commission on Ecosystem Management 2004). As described by the IUCN Commission on Ecosystem Management, ecological restoration has, as its goal, an ecosystem that is resilient and self-sustaining with respect to structure, species

During the 20th and into the 21st Century, federal and state/provincial agencies and conservation organisations played an important role in the conservation and recovery of bison as wildlife. Sixtytwo plains bison and 11 wood bison herds have been established for conservation, representing about 7% of the continental population. In parallel, since about 1980, the number of bison raised under captive commercial propagation has increased markedly, and now represent about 93% of the continental population (Chapter 7).

1.3

Current Challenges for Conservation and Ecological Restoration of Bison as Wildlife

Conservation of any wildlife species requires ensuring both long-term persistence of a sufficient number of populations and maintaining the potential for

Plate 1.1 Free ranging bison in Yellowstone National Park. Photo: John Gross.


composition and function, as well as being integrated into the larger landscape, and supporting sustainable human livelihoods. Ecological restoration involving bison as an integral component of ecosystems faces two major challenges: 1) how to undertake restoration across large areas with diverse land-use and ownership patterns; and 2) how to undertake restoration in a way that improves both biodiversity and human wellbeing. Large-scale ecological restoration involves biological and social complexity. Attitudes, economics and politics, from local to regional and international scales, will shape the future of bison conservation on occupied lands. These challenges are addressed in Chapter 10.

1.5

Conserving the Wild Character and Genome of Bison

Bison in captive herds may be managed to achieve various objectives, including the ecological services that bison provide (e.g., grazing, nutrient cycling, and terrain disturbance), education and display, commercial production, and conservation of bison as wildlife. Conserving bison as wildlife is not necessarily served by managing a population for other purposes. For example, the ecological effects of herbivory may be achieved by grazing a variety of livestock species. Although some rangelands formerly used for cattle production have been converted to bison production, the substitution of bison for cattle production does not, by itself, necessarily contribute to bison conservation, or to ecological restoration of bison as wildlife. Similarly, display herds may serve conservation education objectives without otherwise contributing to species conservation. In the absence of intentional policies and actions to conserve the wild character and genome of bison, captivity and commercialisation can lead inadvertently or intentionally to a variety of effects that may be deleterious to bison as a wildlife species in the intermediate to long term (Chapter 4). These include effects on the genome: founder effect; reduced genetic diversity; persistence and phenotypic penetration of deleterious genes; or inadvertent selection for heritable morphology, tameness or adaptation to captivity. Small populations are particularly susceptible to such effects. The sex and age structure of captive conservation populations may be manipulated to reduce the risk of escape, remove aggressive animals, or to alter fecundity or the rate of population increase. The age composition of males in captive herds is typically substantially different from wild populations. The common practice in captive commercial herds of eliminating males, before they become morphologically and behaviourally mature, poses a challenging question about the roles of mate competition and natural selection for fitness in such populations. In general, selection pressures on captive wildlife

are substantially different from those in the wild. O’Regan and Kitchener (2005) posited that domestication may occur inadvertently in captive wild mammals through passive selection for individuals behaviourally suited to captivity, with concomitant morphological changes over several generations. Most changes are thought to result from increasing paedomorphosis, whereby juvenile characteristics are retained in the adult form of an organism (O’Regan and Kitchner 2005). Clutton-Brock (1999) described changes in large mammals under captive conditions including reduced body and brain size, altered external appearance, the gaining of a fat layer beneath the skin and a reduction of the facial region. Inadvertent selection for tameness and adaptation to a captive environment is typical in mammals (Frankham et al. 1986), and in addition to altering “wildness”, can reduce the chances for successful reintroduction of captives into the wild. A loss of response to predators and alteration of defensive and sexual behaviours have also been reported in captive wildlife (Price 1999; 2002). Many commercial bison producers directly select for marketable traits such as early maturity, coat colour, body size and conformation. The latter “show ring traits” are promoted in bison industry advertisements, publications and at auctions. The large size of the commercial captive population is the basis for a popular misconception that the species is “secure”, leading wildlife management agencies to ignore actions necessary for conservation of wild type bison. Today, among North American jurisdictions, there is a confusing array of classifications of bison as wildlife, domestic livestock, or both (Chapter 8). Hybridisation with cattle is another serious challenge for bison conservation. In the U.S., Canada, and Europe, agricultural interests attempted to develop an improved range animal by hybridising bison and cattle. Forced-mating of bison and cattle can be readily achieved in a controlled environment. However, they preferentially mate with their own species under open range conditions (Boyd 1908; Goodnight 1914; Jones 1907). In Europe, the European bison (Bison bonasus), a relative of the American bison, and the aurochs (Bos taurus primigeneus), progenitor of modern cattle, were sympatric, yet evolutionarily divergent, units. Typical of sympatric species occupying similar trophic niches, behavioural and ecological specialisation provides niche separation, leading to reproductive isolation and progressively to speciation (Bush 1975; Rice and Hostert 1993). Species divergence and reproductive incompatibility are evident from the low fertility of first generation (F1) bison x cattle offspring (Boyd 1908; Steklenev and Yasinetskaya 1982) and the difficulty producing viable male offspring (Boyd 1914; Goodnight 1914; Steklenev and Yasinetskaya 1982; Steklenev et al. 1986). Unfortunately, forced hybridisations between B. bison and Bos taurus in North America have left a legacy of cattle mitochondrial (Polziehn et al. 1995; Ward et al. 1999) and nuclear DNA (Halbert 2003; Halbert et al. 2005). This introgression is


widespread among contemporary bison populations, in both public and private sector herds (Chapter 4). The implications for bison conservation are just beginning to be understood and appropriate interventions considered.

1.6 Reportable Diseases Bison host numerous parasites and pathogens (Reynolds et al. 2003; Tessaro 1989), some of which are important to conservation. Livestock diseases that restrict trade or pose a risk to human health and are ‘reportable’ under federal, provincial, and state legislation are particularly important because they may induce management actions that negatively affect bison conservation and restoration (Chapter 5). Management interventions may include depopulation, limiting dispersal and range expansion to protect adjacent bison or livestock populations, and restraining translocations. The presence or perceived risk of reportable diseases in bison devalues them as wildlife and constrains conservation and recovery potential. Large free-ranging bison populations are infected with exotic (non-native) reportable diseases in two areas of the continent, the Greater Yellowstone Area (GYA) mainly in Montana and Wyoming (bovine brucellosis), and the Greater Wood Buffalo Ecosystem in Alberta and the Northwest Territories (bovine brucellosis and tuberculosis). Balancing conservation with intensive interventions is a perpetual challenge for the agencies responsible for managing these populations.

1.7 Purpose of this Document This document provides an authoritative summary of the biology and status of American bison, including: prehistoric to recent history and cultural context (Chapter 2); taxonomy and related issues (Chapter 3); genetic variation and effects of human interventions on the genome (Chapter 4); diseases that directly or indirectly affect bison conservation (Chapter 5); biology and ecology of the species (Chapter 6); the numeric and geographic status of American bison, emphasizing herds managed primarily for conservation (Chapter 7); legislation and policies pertaining to bison in all range states (Chapter 8). Guidelines for bison conservation are provided in the final two chapters of this document (Chapter 9 Population and Genetics Guidelines; Chapter 10 Ecological Restoration Guidelines). Throughout the document reference is made to challenges requiring actions ranging from urgent to long term. Non-prescriptive guidance is offered on how conservation and ecological restoration of bison as wildlife may be achieved, while respecting the principles of democratic governance in the three nations forming North America, the sustainability of economic use of ecological resources, cultural heritage values, and ecological values of intact ecosystems.


Chapter 2

History of Bison in North America Lead Authors: Ben A. Potter, S. Craig Gerlach, and C. Cormack Gates, Contributors: Delaney P. Boyd, Gerald A. Oetelaar, and James H. Shaw

2.1 Palaeobiology and Phylogeny Bison have existed in various forms for more than 2,000,000 years (Danz 1997; McDonald 1981). Early forms originated in Asia and appear in Villafranchian deposits, and in the early fossil record in India, China, and Europe (Guthrie 1990; Shapiro et al. 2004). Bison occupied Eurasia about 700,000 years ago then moved across the Bering Land Bridge into Alaska during the middle Pleistocene 300,000–130,000 years ago (Illinoin Glaciation; Marine Oxygen Isotope Stages (MIS) 8 to 6 (Shapiro et al. 2004). All Siberian and American bison shared a common maternal ancestor about 160,000 years ago (Shapiro et al. 2004). Fossil evidence indicates there was a single species, or at least a similar large-horned form with variable species/sub-species designations, the steppe bison, Bison priscus, throughout Beringia (Guthrie 1990).

Villafranchian: a major division of early Pleistocene time, named for a sequence of terrestrial sediments studied in the region of Villafranca d’Asti, an Italian town near Turin. This was a time when new mammals suddenly appeared. Holarctic: a term used by zoologists to delineate much of Eurasia and North America, which have been connected by the Bering land bridge when sea levels are low during glacial periods. Plesitocene: Ice Age. A division of geological time; epoch of the Quaternary period following the Pliocene. During the Pleistocene, large areas of the northern hemisphere were covered with ice and there were successive glacial advances and retreats. Beringia: a 1,000 mile wide ice-free grassland steppe, in Asia and North America linked together by the “Bering Land Bridge” when sea levels were low. Animals traveled in both directions across this vast steppe, and humans entered the Americas from what is now Siberia.

Plate 2.1 Skull of Bison priscus, Yukon Canada. Photo: Cormack Gates.

Steppe bison probably reached their maximum distribution and abundance during the last glacial period (Wisconsinan, 100,000– 12,000 years B.P.; MIS 2-4 and 5a-d). These are the typical bison fossils found in the Yukon and Alaska during that period. Steppe bison had relatively long hind legs, similar to the European bison (B. bonasus), and large horns with tips curved back, and a second hump (Guthrie 1990). Analysis of ancient mitochondrial DNA (mtDNA) (Shapiro et al. 2004) suggests that Late Pleistocene bison, found from the Ural Mountains to northern China, were descendants of one or more reverse dispersals from North America. The most recent common ancestor of bison specimens analysed by Shapiro et al. (2004) existed towards the end of the Illinoian Glacial Period (MIS6).

Glacial periods: There have been at least four major ice ages. The present ice age began 40 million years ago with the growth of an ice sheet in Antarctica. Since then, the world has seen cycles of glaciation with ice sheets advancing and retreating on 40,000- and 100,000-year time scales. The most recent glacial period ended about ten thousand years ago. Marine isotopic stages (MIS): alternating warm and cool periods in the Earth’s ancient climate, deduced from oxygen isotope data reflecting temperature curves derived from data from deep sea core samples. Ural Mountains: a mountain range that runs


Phenotype: Observable physical or biochemical characteristics of an organism. Phenotype is determined by both genetic makeup and environmental influences. Clade: A biological group (taxa) that share features inherited from a common ancestor. Holocene: A geological period, which began approximately 11,550 calendar years B.P. (about 9600 BC) and continues to the present. It has been identified with MIS 1 and can be considered an interglacial in the current ice age. Phylogenetics: The study of evolutionary relatedness among groups of organisms. Glacial maximum: The time of maximum extent of the ice sheets during the last glaciation (the Würm or Wisconsin glaciation), approximately 20,000 years ago. Taphonomic processes: The transition of the remains, parts, or products of organisms in soil, e.g. the creation of fossil assemblages through burial. Taxonomy: The science of classification of organisms. Nomenclature is the system of naming

Bison moved south into the grasslands of central North America when the ice sheets retreated at the beginning of the Sangamon Interglacial (MIS 5e) 130,000-75,000 years B.P. (MacDonald 1981), evolving there into a large form, B. latifrons. This giant bison possessed a horn span of more than two metres and was abundant in the central continent during the Sangamon Interglacial. It underwent a gradual reduction in body size and horn span (Guthrie 1980; van Zyll de Jong 1993). During the subsequent Wisconsin Glaciation (110,000-12,000 years B.P.; MIS 2-4 and 5a-d), Beringian and southern populations became separated as the Laurentide continental ice sheet extended into western Canada from 20,000-13,000 years B.P. (Burns 1996; Wilson 1996). Geographic separation had profound biological, taxonomic, and evolutionary effects. Southern bison evolved into distinctive phenotypes (van Zyll de Jong 1993) and separate mtDNA clades. All modern American bison now belong to a single clade that is distinct from Beringean bison, with a most recent common ancestor between 22,000 and15,000 years B.P. (Shapiro et al. 2004). This interpretation is consistent

with complete separation between northern and southern populations at the time of the last glacial maximum (20,00018,000 years B.P.). Data presented by Shapiro et al. (2004) and Wilson et al. (2008) support the hypothesis that modern bison are descended from populations that occurred south of the ice sheet before the Last Glacial Maximum. Southern bison underwent rapid in situ evolution during the early Holocene from B. antiquus to an intermediate form B. occidentalis, then to the modern form B. bison (Wilson et al. 2008). When the continental ice sheets began to melt, bison invaded the emerging ice-free corridor from the south where thawing and melting occurred first. Colonisation from Beringia was limited (Shapiro et al. 2004). Overlap between northern and southern bison occurred in the vicinity of the Peace River in north-eastern British Columbia where northern bison were present by 11,200-10,200 years B.P. (Shapiro et al. 2004), and southern forms of bison were present 10,500 years B.P. Molecular research by Shapiro et al. (2004) indicates that all modern bison are descended from populations living south of the ice sheet before the Last Glacial Maximum. The two modern North American subspecies (plains bison and wood bison) diverged by about 5,000 years ago (Gates et al. 2001; van Zyll de Jong 1986). The wood bison (B.b. athabascae) was the most recent variant to occur in Alaska, the Yukon and Northwest Territories and the plains bison (B.b. bison) is the most recent southern variant of the North American species (van Zyll de Jong 1993 Stephenson et al. 2001). Small-horned bison similar to wood bison also occurred in northern Eurasia during the Holocene (Flerov 1979; Lazarev et al. 1998; van Zyll de Jong 1986, 1993). Although the European bison (B. bonasus) is morphologically similar to and readily interbreeds with the American bison, they form distinctly different clades based on mtDNA sequences of the 273 bp-long fragment of cytochrome b gene (Prusak et al. 2004). This is consistent with geographic separation between these two species starting during the midPleistocene and before reverse-dispersal occurred from North America to Siberia.

2.2

Original Range

Previous typologies divide the Holocene range of bison into “prehistoric” and “historic” periods (van Zyll de Jong 1986). The distinction between them is not based on objective or biologically meaningful criteria, and provides an artificial and confusing temporal dichotomy that persists despite wellinformed arguments to the contrary (Stephenson et al. 2001). A preferred and more accurate alternative is to refer to the previous range of bison as “original” range, thereby avoiding the necessity to distinguish between written records and other sources including zooarchaeological evidence and orally transmitted knowledge (Gates et al. 2001).


Figure 2.1 Original ranges of plains bison and wood bison. Recreated by Boyd (2003) based on van Zyll de Jong (1986) and Stephenson et al. (2001).

Modern bison originally ranged across most of North America (Figure 2.1). Plains bison were most abundant on the Great Plains, but also radiated eastward into the Great Lakes region, over the Allegheny Mountains toward the eastern seaboard, northward as far as northern New England, and then south into Florida; westward, they were found in Nevada and parts of the Great Basin, the Cascade and Rocky Mountains northward to mid-Alberta and Saskatchewan prairie lands, and further south along the Gulf of Mexico into Mexico (Danz 1997; Reynolds et al. 1982). There are records of bison occurring at surprisingly high elevations in mountainous regions, particularly along the Front Range of the Rocky Mountains (Fryxell 1928; Kay and White 2001; Meagher 1986). Evidence also indicates that bison inhabited areas of the Greater Southwest, including Arizona, New Mexico, and northern Mexico, areas not generally recognised as within the original range of plains bison (Truett 1996). Whether apparent or real, bison scarcity in the American Southwest is usually attributed to a combination of insufficient water and grass and human hunting (Truett 1996). The original range of wood bison includes northern Alberta, north-eastern British Columbia, a small area of north-western Saskatchewan, the western Northwest Territories, Yukon, and much of Alaska (Stephenson et al. 2001). More recent research incorporating

oral narratives of aboriginal people in Alaska, Yukon, and Northwest Territories, in combination with archaeological and palaeontological records, demonstrates that wood bison were present in the Yukon and Alaska within the last two centuries, and that these areas are within the original range of the subspecies (Lotenberg 1996; Stephenson et al. 2001).

2.3

Abundance

Historical and archaeological records demonstrate that plains bison thrived on the grasslands of the Great Plains (Malainey and Sherriff 1996; Shaw and Lee 1997). Explorers, settlers, and Euroamerican hunters described enormous herds of plains bison, with population estimates ranging from 15 to 100 million (Dary 1989; Shaw 1995). In the 1890s, naturalist Ernest Thompson Seton posited the widely accepted estimate for American bison at 60 million (Dary 1989; McHugh 1972; Roe 1970; Shaw 1995). Several quantitative and qualitative methods have been used to estimate pre-settlement bison abundance, including direct observation, carrying capacity calculations, and counts of bison killed for market in the late 1800s. Even when used in combination, all methods are fraught with uncertainty, untested,


even unwarranted assumptions, and arbitrary population attributions (Shaw 1995). Regardless, there is little doubt that prior to Euroamerican settlement, plains bison numbered in the millions, and probably even in the tens of millions (Shaw 1995). Wood bison were not as numerous as plains bison owing to limited habitat, although they did inhabit a vast region of the boreal forest in north-western North America (Gates et al. 2001c). Soper (1941) estimated the total wood bison population in 1800 to be 168,000, an estimate that was highly speculative. The Soper estimate is based on the number and distribution of wood bison existing in Wood Buffalo National Park (WBNP) during the 1930s, with some fuzzy extrapolation from the WBNP density to the presumed area of the original wood bison range. The estimate did not account for regional variability in habitat availability. Furthermore, Stephenson et al. (2001) documented a considerably larger original range than Soper (1941). Therefore, wood bison may have been more numerous than estimated by Soper.

2.4

Extirpation

Continental bison numbers declined dramatically and rapidly following European settlement. Specific regional impacts on numbers, distribution, and abundance are recorded in many historical accounts and references (e.g., Dary 1974). Largescale seasonal migrations of both the northern and southern plains bison herds may have temporarily masked their decline, although by the late 1800s it was obvious that the American bison population had been decimated and was in serious decline (Krech 1999). Commercial hunting by Euroamericans and some Native North Americans for meat and hides was a primary cause (Hornaday 1889; Isenberg 2000). The American military quietly approved illicit market hunting on federally protected tribal lands in the northern and southern plains. Other factors included indiscriminate slaughter for sport and recreation. Sport hunting was exacerbated by the westward push of colonization from the east and across the prairies with the implicit and explicit approval of politicians and military leaders anxious to resolve the food supply side of the so-called “Indian problem.” (Danz 1997; Dary 1989; Hewitt 1919; Isenberg 2000; McHugh 1972).

from domestic livestock (horses, cattle, sheep) and wild horses also played a role in reducing bison numbers (Flores 1991; Isenberg 2000). Furthermore, because bison provided sustenance for North American aboriginals and commodities for their barter economy, the elimination of bison was viewed by Euroamericans as the most expedient method to subjugate the Native Americans and force them onto reserves, making way for agrarian settlement and continued western development (Danz 1997; Geist 1996; Isenberg 2000; Mayer and Roth 1958). To this end, the U.S. government unofficially supported the slaughter of bison by providing ammunition and supplies to commercial buffalo hunters (Mayer and Roth 1958). Although an overt political policy to decimate bison was never formally established, the Canadian and U.S. governments capitalised on widespread hunger among aboriginal communities caused by the near extirpation of bison as a means to subjugate and control the aboriginal population (Geist 1996; Stonechild and Waiser 1997). By the late 19th Century it was estimated that there were fewer than 1,000 remaining bison in North America (Hornaday 1889; Seton 1927). Wood bison were concentrated in northern Alberta and the Northwest Territories, and plains bison were scattered in isolated groups across the Central Great Plains and, notably, in what is now Yellowstone National Park (YNP).

2.5

As the great herds diminished, there was some public outcry, but few laws were enacted to protect the bison (Danz 1997). Most early plains bison conservation efforts happened through the independent actions of private citizens. Prominent figures in the conservation movement included James McKay and

Environmental factors, such as regional drought, introduced bovine diseases, and competition Plate 2.2 An enormous pile of bison skulls waiting to be ground for fertilizer (c. mid-1870s). Copyright expired - Courtesy of the Burton Historical Collection, Detroit Public Library - downloaded from English Wikipedia 20 Aug 2009.

Early Recovery


Charles Alloway (Manitoba), Charles Goodnight (Texas), Walking Coyote (Montana), Frederick Dupree (South Dakota), Charles J. Jones (Kansas), and Michel Pablo and Charles Allard (Montana) (Coder 1975; Danz 1997; Dary 1989; Geist 1996). Their efforts to establish herds from the few remaining bison secured the foundation stock for most contemporary public and private plains bison herds. Formed in 1905, the American Bison Society (ABS) pressed Congress to establish several public bison herds at Wichita Mountains National Wildlife Refuge, the National Bison Range (NBR), Sully’s Hill National Game Preserve (SHNGP), and Fort Niobrara National Wildlife Refuge (Coder 1975; Danz 1997). National parks in both the U.S. and Canada also figured prominently in bison recovery efforts (Danz 1997; Ogilvie 1979). Once plains bison were protected from hunting (beginning in the 1870s), their numbers increased considerably, doubling between 1888 and 1902. By 1909, the subspecies was considered safe from extinction (Coder 1975). Initially sparked by nostalgia and reverence for the animal, motivations for bison recovery became increasingly driven by their commercial value (Yorks and Capels 1998). By 1970, there were 30,000 plains bison in North America, with approximately half in public herds located in national parks, wildlife refuges, and state wildlife areas, and half in private herds (Shaw and Meagher 2000). As reviewed in chapter 7, the number of plains bison currently is more than 20,500 in 62 conservation herds, while the number under commercial propagation is about 400,000. The wood bison population fell to a low of 250 animals at the close of the 19th Century, then slowly grew to 1,500-2,000 by 1922 owing to the enforcement of Canadian laws enacted to protect the animal (Gates et al. 2001c; Soper 1941). In 2008, there were about 10,870 wood bison in 11 conservation herds (Chapter 7).

2.6

Cultural Significance

Few species enjoy a history as rich in archaeology, palaeontology, story and legend, oral and documentary history as the American bison. Nor is there another North American species for which the cultural and political significance of an animal is so great. For thousands of years various forms and populations of bison have coexisted with humans in North America, providing sustenance and shaping human social and economic patterns, and influencing national history and international political relationships. Although a comprehensive review of human-bison interactions from the colonisation of North America to recent times is encyclopaedic in scope, a brief summary and discussion is provided here. Bison were important in the subsistence economies of the first Beringian colonisers of the western hemisphere, and later figured prominently, but differentially, in Palaeo-Indian, Archaic,

Palaeo-Indian: (12,000-6,000 B.P.) A group of Late Pleistocene–Early Holocene cultures associated with the colonisation of central North America. While their subsistence economies are debated, many archaeologists consider them to be big game hunting specialists (including mammoth). Folsom: (11,000-10,200 B.P.) A Palaeoindian culture, characterised by very high mobility and specialised bison hunting. Archaic: (6,000-2,300 B.P.) A group of Middle Holocene cultures characterised by broad spectrum foraging (i.e., subsisting on a wide variety of big and small game, fish, shellfish, and plant foods). They do not have permanent villages or agriculture. Plains Woodland: (2,300-1,000 B.P.) A group of Late Holocene cultures characterised by semipermanent villages, horticulture (maize and beans) in addition to hunting and gathering. Altithermal: also the Holocene Climate Optimum. A warm period during the interval 9,000 to 5,000 years B.P. This event is also known by other names, including: Hypsithermal, Climatic and subsequent North American cultural horizons and traditions. Bison were economically and culturally important throughout most of North America, including interior Alaska, Yukon and Northwest Territories, but they were particularly significant for groups living in the Great Plains, from north-central Texas to southern Alberta. Various forms of bison have been identified as key subsistence resources in the Palaeolithic of north-eastern Asia, forming part of a megafaunal complex adapted to the steppe-tundra of Late Pleistocene northern Eurasia and Beringia, along with mammoths and horses (Guthrie 1990). While bison remains are commonly found in Siberian archaeological sites, standard zooarchaeological methods (Ermolova 1978) indicate they do not appear to have contributed greatly to subsistence. By comparison, reindeer, mammoths, and horses are relatively abundant in Siberian archaeological sites. Bison seem to have played a more important role in North American archaeological complexes. In Alaska, there is empirical evidence from numerous archaeological complexes spanning 12,000 to 1,000 years B.P. that links bison with cultural traditions using conservative,


Plate 2.3 Arvo Looking Horse performing a ceremony honouring slaughtered bison after a harvest near Yellowstone National Park. Photo: Jim Peaco, National Park Service.

efficient microblade technology (Holmes and Bacon 1982; Potter 2005; 2008). Microblades are small elongate sharp stone blades inserted into pieces of bone or wood to make composite tools (Guthrie 1983). Bison played a key role in Palaeo-Indian, Archaic, and later economies in North America, particularly in the Great Plains. While some have questioned early Palaeo-Indian dependence on bison and other largebodied ungulates (Grayson and Meltzer 2002), other studies show a clear pattern of specialised large mammal hunting during the Late Pleistocene and Early Holocene in North America (Hofman and Todd 2001; Waguespack and Surovell 2003). Although there are disagreements as to whether Early Palaeo-Indians should be classified as specialised big-game hunters or broad-spectrum foragers, bison evidently played an important role in their subsistence economies. A recent survey by Waguespack and Surovell (2003) reported that 52% of 35 Early Palaeo-Indian components (Clovis, 11,300-10,900 years B.P.) included bison remains. With the extinction of the mammoth and other Pleistocene megafauna, bison became a greater economic focus for late Palaeo-Indian complexes (Folsom and others present during the Early Holocene). Changes in projectile point forms have been linked to specialisations for bison hunting (Stanford 1999). In particular, Folsom complex adaptations have been linked to intensive bison hunting (Amick 1996). Communal bison hunting probably played an important role in seasonal aggregations of PalaeoIndian populations, with human groups combining to hunt and then dispersing into smaller groups in relation to seasonal bison migrations (Kelly and Todd 1988). On the Great Plains, the Holocene Climatic Optimum or Altithermal (about 7,500 years B.P. in mid-latitude North America) resulted in warmer and drier conditions and increased seasonality. Climate change apparently limited bison abundance and geographic distribution, and induced human adaptations to new climatic and ecological conditions (Sheehan 2002; but see Lovvorn et al. 2001). Human populations adjusted primarily by developing new economic strategies, termed “Archaic” by North American archaeologists. Adaptations involved new technologies such as ground stone for processing a variety of plant foods, and incorporating a more diverse array of smaller game and plants into the subsistence economy. During this period, some portions of the Great Plains appear to have been abandoned entirely by people (Meltzer 1999). However, the dearth of sites could also be explained by taphonomy (deep 10

burial or destruction through erosion) (Artz 1996; Walker 1992). Some evidence indicates that during this period bison and people concentrated their activities in localised refugia, such as river valleys (Buchner 1982). Throughout North America, there was a general shift to mixed foraging economies based on more locally abundant resources, with bison playing a much smaller role except in specific areas of the Great Plains. After 2,000 years B.P., archaeological records for the North American grasslands show evidence of widespread human occupation and regional specialisation in habitat use (Manning 1995; Speth 1983). The so-called Plains Woodland complexes showed local patterns of adaptation represented as widespread networks of cultural interactions that linked the eastern woodlands, and perhaps even the Greater Southwest, to the grasslands through trade and religious or ceremonial interactions (Frison 1991). Technologies shifted again to include bows and arrows, pottery and distinctive regional ceramic traditions. Much later, the use of horses formed the basis for the mounted,


nomadic “Plains Indian Culture” observed by European explorers and missionaries at first contact (Duke 1991; Wedel 1959). Native North Americans, during, and even after the Plains Woodland tradition, lived in larger more permanent villages. They depended on maize, bean, and gourd horticulture to name some of the most important domesticates, with winter dependence on deer and seasonal movements in the fall and spring to take advantage of migrating bison herds (Wilson 1987). This pattern is well represented ethnographically in the Middle Missouri Region. Groups like the Siouxan-speaking Mandan and Hidatsa, and the Caddoan-speaking Pawnee and Arikara, with the Wichita and others, were scattered along major Prairie rivers and tributaries like the Loup, Lower Loup, Canadian, and Washita, as far south as Nebraska, Kansas, and Oklahoma (Weltfish 1965). Large kill events, such as those represented at the Head-Smashed-In site in Alberta, generally did not occur until very late in the history of bison hunting on the Plains, and are represented from the Late Archaic and later periods (Byerly et al. 2005). The shift in hunting strategies may have been a response to increasing herd sizes, introduction of bow and arrow, and/or changes in social organisation (Driver 1990; Reeves 1990; Walde 2006). With increased resolution and clarity afforded by ethnohistoric and ethnographic investigations, human-bison interactions among historic native peoples are better described and documented than for the late Pleistocene and Holocene. Bison continued to be the preferred game for many native North American cultures, especially on the Great Plains and Prairies, providing food, clothing, shelter, and tools (Geist 1996; Roe 1970). Sustained by bison and plant resources, many native groups likely affected densities of other large herbivore species (Kay et al. 2000; Martin and Szuter 1999). In addition to significant ecological relationships, the bison was a central element in oral tradition, rituals, dances, and ceremonies of native peoples of the Plains (Wissler 1927), and it remains symbolically important in the cultural traditions of many native Tribes to this day. The arrival of Europeans in North America, after 1492, resulted in significant changes in human-bison interactions, and changed the fabric of Native American life forever. Introduced diseases such as smallpox decimated indigenous human populations (Crosby 1986), and altered subsistence, settlement, demography, and social organisation for many different groups. Bison hunting by native people was seasonal in nature. Bison were incorporated into a broad spectrum of plant and animal procurement activities (Holder 1970; Isenberg 2000). Bison provided the economic basis for stable, resilient land use regimes and social systems. However, effects of Native American warfare and raiding during the historic period disrupted and destabilised these land use and social systems. The spread of horses into Great Plains aboriginal economies by the 1750s, and increasing commoditisation of bison products

caused by the emergence of a European commercial market for wildlife products by the 1820s, contributed to the near extinction of the bison (Flores 1994; Isenberg 2000:27). Native peoples traded bison hides for Euro-american commodities, with the market in bison robes reaching a peak in the 1840s. Hide hunters began to significantly participate in the market hunting of plains bison in the 1850s, and by the 1890s had decimated the herds. Even bones were cleaned for sale to the eastern fertilizer market, an activity that continued to 1906 (Dary 1974). Numerous native North American tribes manage bison on native and tribal lands, but cultural, social and spiritual relationships with this animal are changing. For many Native Americans there is still a strong spiritual and symbolic connection, but for others it is the potential commercial value of bison that is most important. For still others, it is the pragmatic use of bison for food, and the relationship between local control over food production and land, food security, tribal sovereignty, and decreasing reliance on outside sources for food and commodities that is emerging as a topic of concern, and a theme underlying tribal decision-making. It is not just the relationship between Native Americans and bison that is changing, but the role of bison in the overall North American food system is changing as well. The North American perspective is shifting from the view that bison are an artifact from the past to be viewed as such in parks and preserves, to one that sees bison as a dynamic component of the American diet. Along with a new vision for a healthy ecological and genetic future for the American bison, food system researchers, food system enthusiasts, and the biomedical research community envision a new role for bison in the American diet. This role elevates the animal to priority over industrially raised beef and pork, and secures for it a place as the healthy alternative to a fatty, sugar-based diet that already has significant health impacts in terms of increased rates of cardiovascular disease, colorectal and other forms of cancer, and diabetes. Free-range bison meat is higher in omega-3 fatty acids than are grain-fed animals, perhaps even as high as wild salmon and other cold water fish species, and it is also high in conjugated linoleic acid, a fat-blocker and anti-carcinogen with the potential to reduce the risk of cancer, diabetes, and obesity. The extent to which bison can be produced efficiently and in healthy ways that do not further degrade ecosystems and ecosystem services, and marketed as a healthy food at an affordable price, will perhaps be the tipping points for how important bison become in a future American food system. Whether Native American or not, cultural values, attitudes, and perspectives are reflected in how we think about, manage, and handle animals in the wild, in commercial production systems, and after butchering and processing through marketing. Bison are perhaps unique in that we manage them both as wildlife and

American Bison: Status Survey and Conservation Guidelines 2010 11

as livestock, with wood bison in Alaska and Canada an example of the former, and plains bison in the Canadian and American Plains an example of the latter. The jury is probably still out on whether we will manage bison as wildlife, as livestock, or as both in the future, but it is clear that there is a bright role for this animal in an emerging North American food system and tradition. Native Americans are both recovering and restoring their long-established cultural relationship with the American bison, and Native Americans and other non-native North Americans are finding new ways to relate to this animal in ways that will enhance the conservation of the species.

12


Chapter 3

Taxonomy and Nomenclature Lead Authors: Delaney P. Boyd, Gregory A. Wilson, and C. Cormack Gates

The purpose of naming organisms is to facilitate recognition and communication and to identify patterns and apply practical structure to the natural world. Taxonomy can support the conservation and sustainable use of biological diversity by contributing to identification, assessment, and monitoring programmes (Environment Australia 1998). Taxonomy is also vital for the creation and interpretation of laws, treaties, and conservation programmes because it creates legal identities for organisms (Geist 1991). While it is important to strive for accuracy in taxonomic classification, semantic issues and uncertainty can create substantial management challenges by distracting conservation decision makers from the issues threatening a taxon or biological unit worthy of conservation. Despite the extensive history, and the economic and symbolic importance of bison to North American societies, there remains significant confusion and disagreement about bison taxonomy. The issues range from an historical discrepancy over the common name, to ongoing scientific debate over the systematics of the genus, species, and subspecies designations.

3.1

An Historical Misnomer: Bison vs. Buffalo

The bison is not a buffalo. True ‘buffalo’ are native only to Africa (cape buffalo, Syncerus caffer) and Asia (four species of water buffalo, Bubalus spp.). The use of the term buffalo for American bison derived perhaps from other languages used by explorers to describe the unfamiliar beast, e.g., bisonte, buffes, buffelo, buffles, and buffilo (Danz 1997; Dary 1989). These terms are similar to bufle and buffe, which were commonly used to refer to any animal that provided good hide for buff leather (Danz 1997). Despite the misnomer, the term ‘buffalo’ has been used interchangeably with “bison” since early explorers first discovered the North American species (Reynolds et al. 1982). The term has become entrenched as a colloquialism in North American culture and language. Although scientific convention dictates use of ‘bison’, the term ‘buffalo’ persists as an accepted, non-scientific convention for habitual and nostalgic reasons.

3.2

Genus: Bos vs. Bison

When Linnaeus first classified the bison in 1758 for his 10th Edition of the Systema Naturae, he assigned the animal to Bos, the same genus as domestic cattle (Wilson and Reeder 2005). During the 19th Century, taxonomists determined that

there was adequate anatomical distinctiveness to warrant assigning the bison to its own genus (Shaw and Meagher 2000). Therefore, in 1827, C. Hamilton Smith assigned the subgeneric name Bison to the American bison and the European bison (Skinner and Kaisen 1947). In 1849, Knight elevated the subgenus Bison to the level of genus (Skinner and Kaisen 1947). Since then, taxonomists have debated the validity of the genus, some arguing that bison are not sufficiently distinct from cattle, guar, yak, and oxen to warrant a distinct genus (Gardner 2002, personal communication). During the last two decades, as molecular genetic and evolutionary evidence has emerged, scientists have used Bos with increasing frequency. Discrepancies in the genus are reflected in major cataloguing centres and books. For example, the Canadian Museum of Nature (Balkwill 2002, personal communication) and the Smithsonian National Museum of Natural History in its publication Mammal Species of the World (Wilson and Reeder 2005) use Bison, while the Royal Ontario Museum (Eger 2002, personal communication) and the Museum of Texas Tech University, in its Revised Checklist of North American Mammals North of Mexico (Jones, Jr. et al. 1992; Jones et al. 1997; Baker et al. 2003), have reverted to Bos. The debate over the appropriate genus arises from the conflict between the traditional practice of assigning names based on similar features distinguishable by morphology (the phenetic approach) versus using evolutionary relationships (the phylogenetic approach) (Freeman and Herron 2001; Winston 1999). Systematists develop evolutionary trees by analysing shared derived characteristics (Freeman and Herron 2001; Winston 1999). In this scheme, only monophyletic groups, or clades, which represent all descendants of a common ancestor, are named. A phenetic scheme might assign names to partial clades, or paraphyletic groups, which exclude one or more descendants (Freeman and Herron 2001). Some taxonomists and systematists suggest that the traditional naming system be replaced with a phylogenetic scheme (Freeman and Herron 2001). While not all biologists agree this is prudent, given that a strictly phylogenetic scheme could ignore functionally and ecologically important differences among species (Freeman and Herron 2001), the phylogenetic approach provides some useful insights about evolutionary relationships within the family Bovidae. Bison reside in the family Bovidae, subfamily Bovinae, tribe Bovini, which currently contains four genera: Bubalus (Asian water buffalo); Syncerus (African buffalo); Bos (domestic cattle


and their wild relatives), and Bison (bison) (Wall et al. 1992; Wilson and Reeder 2005). Studies of nuclear-ribosomal DNA (Wall et al. 1992), mitochondrial DNA (Miyamoto et al. 1989; Miyamoto et al. 1993), and repetitive DNA sequences (Modi et al. 1996) within this tribe have revealed that the genus Bos is paraphyletic with respect to the genus Bison. Mitochondrial DNA studies do not support the traditional organisation of the tribe Bovini because the yak (Bos grunniens) is more closely related to bison than to its congener cattle (Bos taurus) (Miyamoto et al. 1989; Miyamoto et al. 1993). Ribosomal DNA studies have not fully clarified this relationship (Wall et al. 1992). However, skeletal analysis by Groves (1981) noted that bison and yak have 14 thoracic vertebrae while other members of the Tribe Bovini have only 13, underscoring the importance of considering heritable morphological differences that may not be revealed using molecular methods. A comparison of various phylogenetic trees for the tribe Bovini further illustrates the naming conflict. Figure 3.1(a) depicts a

conventional scheme based on morphological characteristics (Bohlken 1958), while Figures 3.1(b-d) show different interpretations based on cranial or genetic evidence. Although non-conventional schemes do not share identical branching patterns for every species, the position of Bison within the pattern of development for each alternative is equally incongruous. In the conventional scheme, Bos branched off the tree later than Bison; however, the arrangements based on more recent evidence suggest that a Bos branch was followed by Bison, then by Bos. Each alternative demonstrates that Bos is paraphyletic because it is lacking one of its descendant branches (denoted as Bison). Under a phylogenetic scheme, bison would be included in the Bos clade to correct this incongruity. For four decades, there have been suggestions to combine Bison and Bos into one genus (Baccus et al. 1983; Gentry 1978; Groves 1981; Miyamoto et al. 1989; Modi et al. 1996; Stormont et al. 1961; Van Gelder 1977). Studies of DNA, blood types, and chromosomal, immunological, and protein sequences

Figure 3.1 Comparison of phylogenetic hypotheses for the tribe Bovini based on: (a) conventional morphological analysis (Bohlken 1958); (b) cladistic analysis of cranial characteristics (Groves 1981); (c) mtDNA sequences (Miyamoto et al. 1989); and (d) ribosomal DNA analysis (Wall et al. 1992).

14


demonstrate that Bison and Bos were genetically similar, given molecular methods existing at the time (Beintema et al. 1986; Bhambhani and Kuspira 1969; Dayhoff 1972; Kleinschmidt and Sgouros 1987; Stormont et al. 1961; Wilson et al. 1985). Additionally, the percent divergences among mitochondrial DNA (MtDNA) sequences of Bison bison, Bos grunniens, and Bos taurus were comparable to those calculated among other sets of congeneric species assessed until 1989 (Miyamoto et al. 1989). Reproductive information also supports the inference of a close phylogenetic relationship between Bos and Bison; Bison and some members of Bos can hybridise under forced mating to produce partially fertile female offspring (Miyamoto et al. 1989; Van Gelder 1977; Wall et al. 1992; Ward 2000). Species divergence and reproductive incompatibility are evident with the low fertility of first generation (F1) bison x cattle offspring (Boyd 1908; Steklenev and Yasinetskaya 1982) and the difficulty producing viable male offspring (Boyd 1908; Goodnight 1914; Steklenev and Yasinetskaya 1982; Steklenev et al. 1986). Behavioural incompatibility is also evident. Although mating of bison and cattle can readily be achieved in a controlled environment, they preferentially associate and mate with individuals of their own species under open range conditions (Boyd 1908; 1914; Goodnight 1914; Jones 1907). Differences in digestive physiology and diet selection between cattle and American bison (reviewed by Reynolds et al. 2003) and European bison (Gębczyńska and Krasińska 1972) provide further evidence of the antiquity of divergence between cattle and bison. Based on palaeontological evidence, Loftus et al. (1994) concluded that the genera Bos and Bison shared a common ancestor 1,000,000–1,400,000 years ago. In North America, sympatry between bison and cattle is an artefact of the recent history of colonisation by Europeans and their livestock. However, in prehistoric Europe, the wisent (Bison bonasus) and aurochs (Bos taurus primigeneus), the progenitor of modern cattle, were sympatric yet evolutionarily divergent units. The divergence in behaviour, morphology, physiology, and ecology observed between bison and cattle is consistent with the theory that ecological specialisation in sympatric species occupying similar trophic niches provides a mechanism for reducing competition in the absence of geographic isolation (Bush 1975; Rice and Hostert 1993). The assignment of an animal to a genus in traditional naming schemes can be subjective, and changing generic names can create confusion and contravene the goal of taxonomy, which is to stabilise nomenclature (Winston 1999). However, we caution that maintaining a stable nomenclature should not occur at the expense of misrepresenting relationships. A change of Bison to Bos may reflect inferred evolutionary relationships and genetic similarities between Bison and Bos species. It could also potentially provide continuity and stability to the scientific reference for bison, which currently has two species names in use

(B. bonasus and B. bison). However, and in contrast, based on divergence on a cytochrome b gene sequence analysis, Prusak et al. (2004) concluded that although American and European bison are closely related, they should be treated as separate species of the genus Bison, rather than subspecies of a bison species. There is also the potential that changing the genus from Bison to Bos would complicate management of European (three subspecies) and American bison (two subspecies) at the subspecies level and disrupt an established history of public policy and scientific community identification with the genus Bison. Further research and debate by taxonomists and the bison conservation community is required to reconcile molecular, behavioural and morphological evidence before a change in nomenclature could be supported by the American Bison Specialist Group (ABSG). In consideration of the uncertainties explained above, and in keeping with the naming conventions for mammals used for the 1996 Red List and the 2008 Red List (Wilson and Reeder 1993; Wilson and Reeder 2005), the ABSG adheres to the genus Bison with two species, European bison (B. bonasus) and American bison (B. bison), in this document.

3.3

Subspecies

A controversial aspect of American bison taxonomy is the legitimacy of the subspecies designations for plains bison (B. Bison bison) and wood bison (B. bison athabascae). The two subspecies were first distinguished in 1897, when Rhoads formally recognised the wood bison subspecies as B. bison athabascae based on descriptions of the animal (Rhoads 1897). Although the two variants differ in skeletal and external morphology and pelage characteristics (Table 3.1), some scientists have argued that these differences alone do not adequately substantiate subspecies designation (Geist 1991). The issue is complicated by the human-induced hybridisation between plains bison and wood bison that was encouraged in Wood Buffalo National Park (WBNP) during the 1920s. Furthermore, the concept of what constitutes a subspecies continues to evolve. The assignment of subspecific status varies with the organism, the taxonomist, and which of the various definitions of subspecies is applied. Mayr and Ashlock (1991:430) define a subspecies as “an aggregate of local populations of a species inhabiting a geographic subdivision of the range of the species and differing taxonomically from other populations of the species.” Avise and Ball (1990:59-60) adapted their definition from the Biological Species Concept, which defines species as groups of organisms that are reproductively isolated from other groups (Mayr and Ashlock 1991): “Subspecies are groups of actually or potentially interbreeding populations phylogenetically distinguishable from, but reproductively compatible with, other such groups.”


Table 3.1 Comparison of structural and pelage characteristics for the two bison subspecies.

Plains bison Bison bison bison

Wood bison Bison bison athabascae

colouration, also varied along this axis (van Zyll de Jong et al. 1995). Therefore, the continuous gradation of intermediate bison forms prevents definitive recognition of northern and southern forms of plains bison at the trinomial level.

Unlike the clinal variation reported for plains bison, a phenotypic discontinuity exists between plains bison and wood bison (van Zyll de Jong 1993), reflected in size and in morphological differences independent of size (van Zyll Pelage characteristics de Jong 1986; Gates et al. 2001). Discontinuous variation Dense woolly bonnet of hair between horns Forelock dark, hanging in strands over forehead occurs when a barrier impedes gene flow between populations Thick beard and full throat mane, extending Thin beard and rudimentary throat mane of a species, causing genetic below rib cage differences to accumulate on Well-developed chaps Reduced chaps either side of the barrier (van Zyll de Jong 1992). Reproductive Well-demarcated cape, lighter in colour than No clear cape demarcation, hair usually darker isolation caused by differing wood bison than plains bison habitat preferences and seasonal Structural Characteristics movements, and the natural barrier formed by the boreal Highest point of the hump over front legs Highest point of the hump forward of front legs forest, contributed to maintaining the phenotypic differences Horns rarely extend above bonnet Horns usually extend above forelock between plains bison and wood bison (van Zyll de Jong 1986; van Smaller and lighter than the wood bison Larger and heavier than plains bison (within Zyll de Jong 1993; Gates et al. (within similar age and sex classes) similar age and sex classes) 2001). The Society for Ecological Restoration International (SERI) and IUCN Commission on Crucial to this definition is the argument that evidence for Ecosystem Management (2004) explicitly recognise the phylogenetic distinction must derive from multiple concordant, continuous nature of biological processes, such as speciation, independent, genetically-based (heritable) traits (Avise and in its guidelines for restoration of ecosystems that have been “… Ball 1990). Essentially, subspecies should demonstrate several degraded, damaged, or destroyed relative to a reference state or conspicuous morphological differences, geographic allopatric a trajectory through time” (Chapter 9). Analysis of ancient mtDNA population patterns, and normally possess genetic divergences indicates that modern American bison are derived from a most at several genes (Winston 1999). Hybridisation between recent common ancestor existing 22,000 to 15,000 years B.P. subspecies is possible along contact interfaces (Winston 1999). (Shapiro et al. 2004; Chapter 2). The fossil record and observations of variability among The allopatric distribution and quantified phenotypic differences living bison suggest that the species exhibited considerable between the bison subspecies are consistent with the geographic variation. This variation led to claims identifying subspecies concept. Nevertheless, there has been a suggestion various forms of the species, most notably a northern and a that the two subspecies are actually ecotypes, that is, forms southern plains bison, which differed in pelage and conformation exhibiting morphological differences that are simply a reflection (van Zyll de Jong 1993). Analysis of cranial, horn, and limb of local environmental influences rather than heritable traits measurements for plains bison suggests clinal variation along (Geist 1991). This hypothesis is not supported by observations a north-south axis (McDonald 1981; van Zyll de Jong 1993). of transplanted plains and wood bison. Wood bison transplanted It is possible that external characteristics, such as pelage 16


from their original habitat near the Nyarling River in WBNP to very different environments in the Mackenzie Bison Sanctuary (MBS) (in 1963) and Elk Island National Park (EINP) (in 1965) do not differ from each other, or from later specimens taken from the original habitat (van Zyll de Jong 1986; van Zyll de Jong et al. 1995). Furthermore, despite the passing of over 40 years, the EINP wood bison, which live under the same conditions as plains bison residing separately within the park, show no evidence of morphological convergence with the plains bison form (van Zyll de Jong 1986; van Zyll de Jong et al. 1995). Similarly, plains bison introduced to Delta Junction, Alaska (in 1928) from the National Bison Range (NBR) have clearly maintained the phenotypic traits of plains bison (van Zyll de Jong 1992; van Zyll de Jong et al. 1995). Such empirical evidence suggests that the morphological characteristics that distinguish plains and wood bison are genetically controlled (van Zyll de Jong et al. 1995). Hybridisation between the subspecies in WBNP after an introduction of plains bison during the 1920s has complicated the consideration of subspecies designations. The controversial decision to move plains bison from Wainwright Buffalo Park (WBP) in southern Alberta to WBNP (from 1925 to 1928) resulted in the introduction of domestic bovine diseases to wood bison (Chapter 5), and threatened the distinctiveness and genetic purity of the subspecies. In 1957, Canadian Wildlife Service researchers discovered a presumably isolated population of 200 wood bison near Nyarling River and Buffalo Lake. The researchers believed that this herd had remained isolated from the hybrid herds, and therefore, represented the last reservoir of original wood bison (Banfield and Novakowski 1960; Ogilvie 1979; Van Camp 1989). In an effort to salvage the wood bison subspecies, bison from the Nyarling herd were relocated to establish the MBS and EINP wood bison herds in the 1960s. Later analysis has indicated that the Nyarling herd, and bison elsewhere in WBNP and adjacent areas, did have contact with the introduced plains bison (van Zyll de Jong 1986; Aniskowicz 1990), but it was minimal enough that the animals continued to exhibit predominately wood bison traits (van Zyll de Jong et al. 1995). Studies on the impact of the plains bison introduction have determined that the hybridisation did not result in a phenotypically homogeneous population, as was feared (van Zyll de Jong et al. 1995). Sub-populations within WBNP demonstrate varying degrees of plains bison traits depending on their proximity to, or ease of access from, the original plains bison introduction site (van Zyll de Jong et al. 1995). Although descriptive morphology and quantitative morphometry provide substantial evidence supporting the subspecific designations (van Zyll de Jong et al. 1995), early analysis of blood characteristics and chromosomal homology did not detect a difference (Peden and Kraay 1979; Stormont et al. 1961; Ying and Peden 1977). Preliminary analysis of growth regulating

genes within the two subspecies suggests that the bison subspecies have reached a stage of evolutionary divergence due to geographic isolation (Bork et al. 1991); however, under the Biological Species Concept, subspecies may be defined at the next stage of speciation, that is when hybrid offspring exhibit reduced fitness, which does not appear to be the case in WBNP (Bork et al. 1991). Furthermore, analysis of mtDNA from Nyarling River wood bison and plains bison did not produce monophyletic groups (Strobeck 1991; 1992). This, however, does not mean that there is no difference. In isolated populations, mtDNA diverges at a rate of 1 to 2% per million years (Wilson et al. 1985). It is estimated that the two bison subspecies diverged approximately 5,000 years ago (van Zyll de Jong 1993; Wilson 1969), and human-induced subspecies hybridisation further complicated the phylogeny. Therefore, current genetic analysis techniques may not be able to detect existing differences in the mitochondrial genome. In addition, because mtDNA is maternally inherited, mtDNA within the Nyarling River herd, as well as other herds in WBNP, reflects the contributions from maternal populations, which had a biased representation of plains bison cows (Gates et al. 2001). Therefore, the inability to detect a difference with a molecular test comparing limited sequences of genomic material does not necessarily mean there is no genetic difference; it may just be beyond the current resolution of technology. Recent studies of DNA microsatellites indicate that the genetic distances between plains bison and wood bison are greater than those within either of the two subspecies (Wilson 2001; Wilson and Strobeck 1999). The wood bison populations studied formed a distinctive group on a Nei’s minimum unrooted tree; a strong grouping despite the pervasive hybridisation with plains bison (Wilson 2001; Wilson and Strobeck 1999). Wilson and Strobeck (1999) and Wilson (2001) concluded such a strong clustering indicates wood bison and plains bison are functioning as distinct genetic entities, and should continue to be managed separately. Based on the available evidence, Canada’s National Wood Bison Recovery Team concluded: (1) historically, multiple morphological and genetic characteristics distinguished wood bison from the plains bison; (2) wood bison and plains bison continue to be morphologically and genetically distinct, despite hybridisation; and (3) wood bison constitute a subspecies of bison, and therefore, should be managed separately from plains bison (Gates et al. 2001). The issue of subspecies designations is relevant to conservation in that a decision to combine forms at the species level would invite hybridisation and effectively eliminate any evolutionary divergence that had occurred. Establishing definitive recognition of bison subspecies is complicated by ongoing change of genus, species and subspecies concepts (Winston 1999). However, other classifications and concepts, such as the evolutionarily significant unit (ESU; Ryder 1986), and genetic and ecological


exchangeability, move beyond traditional trinomial taxonomy to incorporate evolutionary considerations. Conservation biologists are reconsidering definitions of conservation units that incorporate both the history of populations reflected in molecular analysis, and adaptive differences revealed by life history and other ecological information (Crandall et al. 2000; DeWeerdt 2002). For example, the geminate evolutionary unit identifies conservation units that are genetically similar but ecologically or behaviourally distinct (Bowen 1998). Crandall et al. (2000) argue for a broad categorisation of population distinctiveness based on non-exchangeability of ecological and genetic traits. Each of these concepts presents challenges, as does any concept that attempts to divide the biological continuum for the convenience of human interests. Essentially, differentiation on any level within a species warrants a formal decision and recognition. Of note, The U.S. Endangered Species Act recognises this conservation issue and provides for protection of “distinct population segments”. Similarly, the Committee on the Status of Endangered Wildlife in Canada (COSEWIC), which is responsible for assessing the status of wildlife, includes any indigenous species, subspecies, variety or geographically defined population of wild fauna or flora as a “species”. While there appear to be sufficient grounds for formal recognition of American bison subspecies, the debate may continue. This, however, should not preclude conservation of the two forms as separate entities (van Zyll de Jong et al. 1995; Wilson and Strobeck 1999). Regardless of current genetic,

18

biochemical or other evidence about the subspecies question, there are notable phenotypic differences, and potentially other types of variation that may not be detectable with technologies available at this time. Geneticists predict that genetic analysis in the future will be able to better identify groupings within species (Wilson 2001). Although genetic and morphological evidence often correspond, this is not always the case (Winston 1999). This can lead to debate over recognising variation that cannot be measured using alternative morphological or molecular methods. Nevertheless, all forms of geographic and ecological variation within a species contribute to biodiversity (Secretariat of the Convention on Biological Diversity 2000). All variants of a species may carry evolutionarily important ecological adaptations (Chapter 4), and possess the potential to develop genetic isolating mechanisms leading in evolutionary time to new species (O’Brien and Mayr 1991). Prediction of which variants will evolve to become species is not possible; this is an outcome of natural selection and chance. Therefore, to maintain biodiversity and evolutionary potential, it is important to not dismiss any form of differentiation within a species, and to maintain the opportunity for evolutionary processes to function (Crandall et al. 2000). Debating whether a name is warranted within a relatively arbitrary taxonomic system does not absolve humans of the responsibility to recognise and maintain intraspecific diversity as the raw material of evolution. The risk of losing evolutionary potential suggests it would not be prudent to prematurely dismiss existing groupings such as the plains and wood bison.


Chapter 4

Genetics Lead Authors: Delaney P. Boyd, Gregory A. Wilson, James N. Derr, and Natalie D. Halbert

As a science, population genetics is concerned with the origin, nature, amount, distribution and fate of genetic variation present in populations through time and space. Genetic variation constitutes the fundamental basis of evolutionary change and provides the foundation for species to adapt and survive in response to changing intrinsic and extrinsic stressors. Therefore, loss of genetic diversity is generally considered detrimental to long-term species survival. In the short-term, populations with low levels of genetic diversity may suffer from inbreeding depression, which can increase their probability of extirpation and reduce fitness. Plains and wood bison experienced severe and well-documented population declines in the 19th Century that reduced the census size of this species by over 99.99%. The spectacular recovery to around 430,000 animals today (Chapter 7) is a testament to their genetic constitution, and represents one of the most significant accomplishments in modern conservation biology. American bison have, however, undergone artificial hybridisation with domestic cattle, been subjected to domestication and artificial selection, and been separated into many relatively small isolated populations occupying tiny fractions of their original range. As well, all wood bison populations contain some level of plains bison genetic material due to artificial hybridisation between the subspecies. All of these factors have had an effect on the current levels of genetic diversity and on the integrity of the bison genome. As a result, preservation of bison genetic diversity is a key longterm conservation consideration. The following sections discuss some of the major issues that are important for the genetic management of this species into the future.

4.1 Reduction of Genetic Diversity Within species, genetic diversity provides the mechanism for evolutionary change and adaptation (Allendorf and Leary 1986; Chambers 1998; Meffe and Carroll 1994; Mitton and Grant 1984). Reduction in genetic diversity can result in reduced fitness, diminished growth, increased mortality of individuals, and reduced evolutionary flexibility (Allendorf and Leary 1986; Ballou and Ralls 1982; Franklin 1980; Frankham et al. 1999; Mitton and Grant 1984;). There are four interrelated mechanisms that can reduce genetic diversity (heterozygosity and number of alleles): demographic bottlenecks, founder effects, genetic drift, and inbreeding (Meffe and Carroll 1994). Unfortunately, over the last two centuries, bison in North America have, to some degree, experienced all of these mechanisms.

As American bison approached extinction in the late 1800s, they experienced a severe demographic bottleneck, leading to a concern that extant bison populations may have lower genetic diversity than pre-decline populations. The consequences of a genetic bottleneck depend on the pre-bottleneck genetic diversity within a species, the severity of the decline, and how quickly the population rebounds after the bottleneck (Meffe and Carroll 1994; Nei et al. 1975). The decline of bison was severe, with a reduction from millions to fewer than 1,000 individuals. Recovery efforts, however, enabled bison populations to grow quickly, more than doubling between 1888 and 1902 (Coder 1975). Although the effects of the bottleneck on the genetic diversity of the species are not clear (Wilson 2001), there are several possible repercussions. First, after a severe reduction in population size, average heterozygosity is expected to decline (Allendorf 1986; Nei et al. 1975). Heterozygosity is a measure of genetic variation that is a direct reflection of the past breeding history of a population. Heterozygosity values are expressed as the frequency of heterozygotes (i.e., genes with dissimilar alleles) expected at a given locus (Griffiths et al. 1993). A reduction in the level of heterozygosity can result in inbreeding effects. At the same time, a loss of alleles may limit a population’s ability to respond to natural selection forces and reduce the adaptive potential of a population (Allendorf 1986; Meffe and Carroll 1994; Nei et al. 1975; Robertson 1960). After the demographic crash, several small bison herds remained in North America, many of which were derived from very few animals. Overall levels of genetic variation in current populations can, in theory, vary directly with the number of original founders (Meffe and Carroll 1994; Wilson and Strobeck 1999). Remnant populations may not have been representative of the original gene pool and, consequently, suffered reduced genetic variability. Through time, the detrimental effects of genetic drift may have compounded the effects of the earlier bottleneck. Genetic drift involves the random change in gene frequencies and leads to the loss of alleles over time. The rate of this loss, or fixation of alleles, is roughly inversely proportional to the population size (Allendorf 1986; Meffe and Carroll 1994). However, the actual count of breeding individuals in a population is not appropriate for determining the rate of genetic drift because factors such as unequal sex ratios, differential reproductive success, overlapping generations, and non-random mating result in the “effective” population size always being less than the census size. For bison, the ratio of effective population size (Ne) to the census population size (N) has most commonly


been estimated to be between 0.16 and 0.42 (Berger and Cunningham 1994; Shull and Tipton, 1987; Wilson and Zittlau, 2004), although Shull and Tipton (1987) suggested that the ratio could be as low as 0.09 in some managed populations. It is possible that American bison experienced reductions in overall genetic diversity due to the population bottleneck of the late 1800s; however, this effect may not have been as great as once expected. McClenaghan, Jr. et al. (1990) found that plains bison have greater genetic variability than several other mammals that experienced severe demographic bottlenecks. Furthermore, Wilson and Strobeck (1999), Halbert (2003) and Halbert and Derr (2008) found levels of DNA microsatellite variability in bison populations to be similar to other North American ungulates. Some authors speculate that prior to the bottleneck, the American bison, with the possible exception of the wood bison, expressed surprising homogeneity despite its extensive range (Roe 1970; Seton 1910). Plains bison ranged over large areas. This suggests that extensive animal movements, and thereby gene flow, may have existed among populations (Berger and Cunningham 1994; Wilson and Strobeck 1999). Similar to other large mammals, bison are expected to be less genetically diverse than small mammals (Sage and Wolff 1986). Despite founder effects and low gene flow, which increase genetic distance values, recent studies demonstrate that the genetic distances between existing bison herds are lower than expected, indicating that existing isolated populations are likely derived from one large gene pool (Wilson and Strobeck 1999). Furthermore, foundation herds for contemporary bison originated from across the species’ range, suggesting that much of the pre-existing diversity was likely retained (Halbert 2003). Analysis of ancient DNA may provide an opportunity for assessing pre-bottleneck genetic diversity for comparative purposes (Amos 1999; Cannon 2001; Chambers 1998). Unfortunately, it is not possible to recover the genetic material lost as a result of the bottleneck underscoring the importance of maintaining existing genetic diversity while minimising any future genetic erosion. Inbreeding, or the mating of related individuals, can lead to the expression of deleterious alleles, decreased heterozygosity, lower fecundity, and developmental defects (Allendorf and Leary 1986; Berger and Cunningham 1994; Lande 1999; Meffe and Carroll 1994). Inbreeding is difficult to assess and does not always have measurable deleterious consequences (Berger and Cunningham 1994; Meffe and Carroll 1994); however, it remains a potential cause of reduced diversity in bison. To decrease the effects of inbreeding, some bison herds were founded or augmented with animals from different regions (Wilson 2001). Over time, the translocation of animals among herds may have reduced the impacts of inbreeding and founder effects, which are most severe in isolated, small populations with low levels of genetic diversity. While few bison herds have truly exhibited signs thought to be the result of inbreeding depression, such 20

as high rates of physical abnormalities, reduced growth rates, and reduced fertility, inbreeding depression has been linked to low levels of calf recruitment and high levels of calf mortality in a plains bison herd (Halbert et al. 2004; 2005), and has been suggested to affect male reproductive success in another population (Berger and Cunningham 1994). Although existing bison populations may be derived from a largely homogeneous gene pool, recent studies using DNA microsatellites reveal that several plains bison herds are genetically distinguishable (Halbert and Derr 2008; Wilson and Strobeck 1999). This raises the issue of whether conservation herds should be managed as a large metapopulation, with translocation of bison among herds to maintain local diversity, or as closed herds to preserve emerging localized differentiation. Some populations may be adapting to non-native habitats or changing conditions in the natural environment, and would, therefore, benefit from localized differentiation. Other populations may be adapting to, or inadvertently selected for, unnatural conditions, and would benefit from periodic augmentation (Wilson et al. 2002b). A precautionary approach may be to diversify conservation efforts by transferring randomly selected animals among some herds, to maximise intrapopulation genetic diversity, while maintaining other herds as closed populations with the possibility of the establishment of satellite populations to increase overall effective population sizes (Halbert and Derr 2008). Managers should carefully consider the implementation of metapopulation management plans as a tool to preserve genetic diversity due to historical differences in morphology, behaviour, physiology, and disease status (Lande 1999; Ryder and Fleischer 1996; Wilson et al. 2002b) and to limit the spread of domestic cattle genes between bison populations (Halbert et al. 2005a; 2006). Genetic analysis could be used to monitor genetic diversity by building an inventory of diversity held within conservation herds. There are several measures of genetic diversity including heterozygosity, alleles per locus, and proportion of polymorphic loci (Amos 1999; Templeton 1994; Wilson et al. 2002b). While early work on bison genetics involved blood groups (Stormont 1982; Stormont et al. 1961), some authors suggest that such studies are inappropriate for assessing genetic diversity because selection for blood group type may be high, violating the assumption of selective neutrality (Berger and Cunningham 1994; Knudsen and Allendorf 1987; Yamazaki and Maruyama 1974). More recent studies have used allozymes (Knudsen and Allendorf 1987; McClenaghan et al. 1990), mitochondrial DNA (MtDNA) (Polziehn et al. 1996), nuclear DNA restriction fragment length polymorphisms (Bork et al. 1991), and DNA microsatellites (Wilson and Strobeck 1999) to assess diversity. Investigation of individual genomic regions can reflect overall diversity, allowing for data from various techniques to be combined to provide an accurate representation of genetic diversity (Chambers 1998).


Selection for diversity in one system, such as blood group proteins, or biased selection for maintaining specific rare genetic characteristics could lead to reduced diversity in other parts of the genome (Chambers 1998; Hedrick et al. 1986). Biased selection for maintaining rare alleles is especially questionable if it is not known what the rare allele does, or if it is detrimental (i.e., it may be rare because it is being expunged from the bison genome through natural selection). Variation throughout the genome, rather than the maintenance of one specific rare allele, conveys evolutionary flexibility to a species (Chambers 1998; Vrijenhoek and Leberg 1991). Therefore, it is crucial for a genetic management plan to consider all available measures for managing genetic diversity in the policies and procedures for breeding and culling decisions. An assessment of overall genetic diversity should examine at least 25-30 loci distributed across the nuclear genome (Chambers 1998; Nei 1987). While genetic diversity for some herds has been assessed (Baccus et al. 1983; Berger and Cunningham 1994; Knudsen and Allendorf 1987; Wilson and Strobeck 1999), these studies did not include a sufficient number of loci and comparisons between studies are not possible due to differences in marker systems (allozymes vs. microsatellites). Other studies have included larger numbers of loci and populations; however, several conservation herds have not been fully examined (e.g., some U.S., Canadian and Mexican state, federal and private bison herds; Halbert 2003; Halbert and Derr 2008). Clearly it is important to create a more complete assessment of bison genetic diversity to allow for more informed management decisions. In general, maintaining genetic diversity of American bison requires an understanding of herd population dynamics to assess the probability of long-term persistence of that diversity. Most bison populations are composed of fewer than 1,000 individuals, and it is possible for a relatively small number of dominant males to be responsible for a high percent of the mating in a given year (Berger and Cunningham 1994; Wilson et al. 2002; Wilson et al. 2005; Halbert et al. 2004). This, in turn, can reduce genetic diversity over time, especially in the absence of natural migration and exchange of genetic diversity among populations (Berger and Cunningham 1994). The potential for disproportionate reproductive contributions emphasises the importance of maintaining large herds with large effective population sizes, that given proper management, will prevent loss of genetic diversity (Frankham 1995; Franklin 1980). Assessment of genetic uncertainty, based on Ne, founder effects, genetic drift, and inbreeding, is a required component of a population viability analysis (PVA) (Gilpin and Soulé 1986; Shaffer 1987).

4.2 Hybridisation Hybridisation involves the interbreeding of individuals from genetically distinct groups, which can represent different species, subspecies, or geographic variants (Rhymer and Simberloff 1996). Some authors argue that hybridisation is a potentially creative evolutionary force, which generates novel combinations of genes that can help species adapt to habitat change, although such hybrids often experience reduced fitness (Anderson and Stebbins 1954; Lewontin and Birch 1966; Hewitt 1989). Hybridisation through artificial manipulation or relocation of animals, however, can compromise genetic integrity through genetic swamping of one genome over another and disruption of locally adapted gene complexes (Avise 1994). It can also produce offspring that are devalued by the conservation and legal communities (O’Brien and Mayr 1991; Chapter 7). The genetic legacy of introducing plains bison into a wood bison population in northern Canada, and crossbreeding bison and cattle, have made hybridisation a controversial topic in bison conservation.

4.2.1 Plains bison x wood bison Based on their geographic distribution and morphology, plains bison and wood bison were historically distinct entities (Chapter 3). It can be argued that the introduction of plains bison into range occupied by wood bison was a “negligible tragedy” (Geist 1996), because some consider the two groups to be ecotypes (Geist 1991). Others maintain that the interbreeding of these two types should have been avoided to preserve geographic and environmental variation (van Zyll de Jong et al. 1995). The introduction of either subspecies into the original range of the other could, in theory, erode the genetic basis of adaptation to local environmental conditions (Lande 1999). Therefore, hybridisation between plains and wood bison should be considered detrimental to maintaining the genetic integrity and distinctiveness of these two geographic and morphologically distinct forms. While historically there may have been natural hybridisation events between the subspecies in areas of range overlap, the current hybridisation issue is the consequence of an ill-advised and irreversible decision made nearly 85 years ago. In 1925, the Canadian government implemented a plan to move more than 6,000 plains bison from the overcrowded Wainwright National Park to Wood Buffalo National Park (WBNP). Biological societies from U.S. and Canada strenuously challenged this action, as interbreeding would eliminate the wood bison form, resulting hybrids might not be as fit for the environment, and diseases such as bovine tuberculosis (BTB) would spread to formerly healthy animals (Howell 1925; Harper 1925; Lothian 1981; Saunders 1925). Proponents of the plan countered the criticism by questioning the subspecies designations, arguing


Plate 4.1 Hereford x bison hybrid; cattle gene introgression is morphologically evident. Photo: Bob Heinonen.

that the introduction site was isolated from, and unused by, the wood bison population, and suggesting that the introduced animals were too young to carry BTB (Fuller 2002; Graham 1924). These arguments did not consider the future habitat needs of the growing wood or plains bison populations, nor the likelihood that the two subspecies would not remain isolated. As well, a recommendation that only yearlings that passed a tuberculin test be shipped to WBNP was rejected (Fuller 2002). It was not until 1957 that the discovery of a seemingly isolated herd of 200 animals near the Nyarling River and Buffalo Lake alleviated fears that wood bison was lost to hybridisation (van Camp 1989). Canadian Wildlife Service researchers determined that these animals were morphologically representative of wood bison (Banfield and Novakowski 1960). To salvage the wood bison subspecies, bison from the Nyarling herd were captured and relocated to establish two new herds. Sixteen animals were moved to the MBS north of Great Slave Lake in 1963 (Fuller 2002; Gates et al. 2001c), and 22 animals were successfully transferred to Elk Island National Park (EINP) east of Edmonton, Alberta in 1965 (Blyth and Hudson 1987). Two additional calves were transferred to EINP between 1966 and 1968 (Blyth and Hudson 1987; Gates et al. 2001c). Of those bison transferred, 11 neonates formed the founding herd. Subsequent studies revealed that there was contact between the Nyarling herd and the introduced plains bison (van Zyll de Jong 1986). Although hybridisation within WBNP did not result in a phenotypically homogenous population (van Zyll de Jong et al. 1995), genetic distances among subpopulations in the park are small, indicating that there is gene flow and influence of the plains bison genome throughout all regions of the park (Wilson 2001; Wilson and Strobeck 1999). Despite hybridization, genetic distances between plains and wood bison are generally greater than those observed within subspecies. Moreover, wood bison form a genetic grouping on a Nei’s minimum unrooted tree, suggesting genetic uniqueness (Wilson 2001; Wilson and Strobeck 1999). Morphological and genetic evidence suggest that care should now be taken to maintain separation between these historically differentiated subspecies. Efforts are in place to ensure representative wood bison and plains bison herds are isolated from each other to prevent future hybridisation between these important conservation herds (Harper et al. 2000). 22

4.2.2

Domestic cattle x bison

The concept of crossing bison with domestic cattle dates back to Spanish colonisers of the 16th Century (Dary 1989). There are many accounts of historical attempts to hybridise bison and cattle (Coder 1975; Dary 1989; Ogilvie 1979; McHugh 1972; Ward 2000). Private ranchers involved with salvaging bison had aspirations to combine, through hybridisation, the hardiness and winter foraging ability of bison with the meat production traits of cattle (Dary 1989; Ogilvie 1979; Ward 2000). The Canadian government actively pursued the experimental production of crossbred animals from 1916-1964 (Ogilvie 1979; Polziehn et al. 1995). Historical crossbreeding attempts have created a legacy of genetic issues related to the introgression of cattle DNA into bison herds. Introgression refers to gene flow between populations caused by hybridisation followed by breeding of the hybrid offspring to at least one of their respective parental populations (Rhymer and Simberloff 1996). The introgressed DNA replaces sections of the original genome, thereby affecting the genetic integrity of a species, and hampering the maintenance of natural genetic diversity. Many contemporary bison herds are founded on, and supplemented with, animals from herds with a history of hybridisation (Halbert 2003; Halbert et al. 2005a; 2006; Ward et al. 1999; 2000). This extensive history of hybridisation between these two species raises questions about the integrity of the bison genome and the biological effects of cattle DNA introgression. Fertility problems thwarted many of the original crossbreeding attempts because crosses result in high mortality for offspring and mother (Ward 2000). Experimentation has revealed that crosses of bison females with domestic cattle males produce less mortality in the offspring than the more deadly reverse


cross, however, the latter is more common because it is very difficult to compel domestic cattle bulls to mate with bison females. All F1 generation hybrids experience reduced fertility and viability relative to either parent: F1 males are typically sterile, but the fertility of F1 females makes introgressive hybridisation possible (Ward 2000). Genetic studies have found no evidence of cattle Y-chromosome introgression in bison, which is supported by the sterility of F1 hybrid males from the cross of cattle males with bison females, and by the behavioural constraint preventing domestic bulls from mating with female bison (Ward 2000). However, a number of studies using modern molecular genetic technologies have reported both mtDNA and nuclear DNA introgression in plains bison from domestic cattle. The first of these studies (Polziehn et al.1995) found cattle mtDNA among Custer State Park plains bison. Subsequently, more comprehensive examinations of public bison herds revealed cattle mtDNA in seven of 21 bison conservation herds (Ward 2000; Ward et al. 1999), suggesting that hybridisation issues between these two species were widespread and a significant concern to long-term bison conservation efforts. Further investigations based on high-resolution nuclear DNA microsatellites detected domestic cattle nuclear DNA markers in 14 of these 21 U.S. federal conservation herds (Ward 2000). All major public bison populations in the U.S. and Canada have now been examined using mtDNA, microsatellite markers, or a combination of these two technologies. Combining evidence from both mtDNA and nuclear microsatellite markers with information regarding population histories provides a more complete view of hybridisation between the two species. To date, no genetic evidence of domestic cattle introgression has

been reported in nine of these conservation populations (plains bison unless otherwise noted; n = sample size examined): EINP (wood bison, n = 25); MBS (wood bison, n = 36); WBNP (wood bison, n = 23); EINP plains bison (n = 25); GTNP (n = 39); HMSP (n = 21); SHNGP (n = 31); Wind Cave National Park (WCNP)(n = 352); and YNP (n = 520) (Halbert et al. 2005a; 2006; Ward et al. 1999). However, the ability to detect nuclear microsatellite DNA introgression is highly dependent on the number of bison in each population, the number of bison sampled from each population and the actual amount of domestic cattle genetic material present in the population (Halbert et al. 2005a). Considering statistical confidence (greater than 95%) allowed by detection limits of the technology (Halbert et al. 2006), adequate numbers of bison have been evaluated from only two of these herds that displayed no evidence of hybridisation (WCNP and YNP). These two herds represent less than 1.0% of the 420,000 plains bison in North America today (Freese et al. 2007; Chapter 7) and both of these herds are currently providing animals for the establishment of new satellite herds for conservations efforts (Chapter 7). Further evaluation is urgently needed to more accurately assess levels of domestic cattle genetics in other public bison herds. Hybridisation issues with domestic cattle must be considered along with other genetic and non-genetic factors in determining which populations are designated as ‘conservation herds’. For example, although some public herds are known to have low levels of domestic cattle genetics, these herds may also represent distinct lineages that reflect historical and geographic differences in genetic diversity (Halbert 2003; Halbert and Derr 2006; Halbert and Derr submitted). Caution is needed in longterm conservation planning to ensure that genetic diversity that represents historical bison geographic differences is identified and conserved for all important populations and not just those thought to be free of domestic cattle introgression. Nevertheless, defining genetic histories that include hybridisation is a first step in developing a species-wide conservation management plan. Given that there are several substantial bison herds that appear to be free of cattle gene introgression, it is of paramount importance to maintain these herds in Plate 4.2 Custer State Park plains bison bull; a high level of cattle gene introgression is not morphologically evident. Photo: Cormack Gates.


reproductive isolation from herds containing hybrids.

4.3

Domestication

The number of bison in commercial herds has grown rapidly over the past five decades as many ranchers enter the bison industry to capitalise on the economic opportunities offered by this species (Dey 1997). The increase in commercial bison production may reflect the recognition of the advantages afforded by the adaptations and ecological efficiency of bison as an indigenous range animal. Bison possess several traits that make them preferable to cattle as a range animal, including a greater ability to digest low quality forage (Hawley et al. 1981; Plumb and Dodd 1993), the ability to defend against predators (Carbyn et al. 1993), the ability to survive harsh winter conditions, and a low incidence of calving difficulties (Haigh et al. 2001). According to federal government surveys, the commercial bison population in North America is about 400,000, divided almost equally between the U.S. and Canada (Chapter 7). Despite the current plateau in beef and bison meat prices, both the Canadian Bison Association and the U.S.-based National Bison Association predict very favourable long-term growth of the bison industry. The number of bison in conservation herds is currently estimated at only 20,504 plains bison and 10,871 wood bison. Therefore, approximately 93% of American bison are under commercial production and experiencing some degree of domestication. Domestication is a process involving the genotypic adaptation of animals to the captive environment (Price 1984; Price and King 1968). Purposeful selection over several generations for traits favourable for human needs, results in detectable differences in morphology, physiology, and behaviour between domestic species and their wild progenitors (Darwin 1859; Clutton-Brock 1981; Price 1984). Humans have practiced domestication of livestock species for at least 9,000 years (Clutton-Brock 1981). As agriculture precipitated the settlement of nomadic human cultures, the domestication of several wild mammal species made livestock farming possible (Clutton-Brock 1981). Intensive management practices and competition between domesticated animals and their wild ancestors often pushed wild varieties and potential predators to the periphery of their ranges or to extinction (Baerselman and Vera 1995; Hartnett et al. 1997; Price 1984). Examples of extinct ancestors of domesticated animals include the tarpan (Equus przewalski gmelini), the wild dromedary (Camelus dromedarius), and the aurochs (Bos primigenius) (Baerselman and Vera 1995). The domestication of cattle provides a relevant history from which to consider the issues of bison domestication. Before cattle (Bos taurus) were introduced to North America they had experienced thousands of years of coevolution with human cultures in Europe (Clutton-Brock 1981; Hartnett et al. 1997). During the domestication process cattle were selected for 24

docility and valued morphological and physiological traits, but not without adverse consequences. Genetic selection has produced an animal that is dependent on humans, is unable to defend itself against predators, and has anatomical anomalies, such as a smaller pelvic girdle, which cause calving and walking difficulties (Kampf 1998; Knowles et al. 1998; Pauls 1995). Domestication has altered the wild character of cattle, producing animals maladapted to the natural environment. Furthermore, because the aurochs, the wild ancestor of European domestic cattle, became extinct in 1627 (Silverberg 1967), domestic cattle have no wild counterpart to provide a source of genetic diversity for genetic enhancement and maintenance. While it has been suggested that domesticated animals can be reintroduced into the wild and revert to a feral state (Kampf 1998; Lott 1998; Turnbull 2001), such attempts do not restore the original genetic diversity of a species (Price 1984; van Zyll de Jong et al. 1995). Experience has shown that recovery of original genetic diversity is difficult or impossible once domestic breeds are highly selected for specific traits and wild stocks are extinct (Price 1984; Turnbull 2001; van Zyll de Jong et al. 1995). For example, in the 1920s, two German brothers, Heinz and Lutz Heck, set out to “re-create” the aurochs by back-breeding domestic cattle with other cattle demonstrating aurochs-like qualities (Fox 2001; Silverberg 1967; Turnbull 2001). They produced one successful line, the Hellabrunn breed, also known as Heck cattle. This is an animal that looks very much like an aurochs, but is devoid of the wild traits and hardiness of the original wild form (Fox 2001; Silverberg 1967). This illustrates that the original wild genotype is no longer available to the cattle industry for improving domestic breeds. The history of the aurochs offers a lesson for bison: domestication can lead to altered genetically based behaviour, morphology, physiology, and function, and the loss of the wild type and the genetic diversity it contains. The primary goal of many commercial bison ranchers is to increase profits by maximising calf production, feed-to-meat conversion efficiency, and meat quality (Schneider 1998). This requires non-random selection for traits that serve this purpose, including conformation, docility, reduced agility, growth performance, and carcass composition. Selection for these traits reduces genetic variation and changes the character of the animal over time (Schneider 1998). Although a growing number of consumers prefer naturally produced meat products without hormones, antibiotics, or intensive management (Morris 2001), the demand for bison cannot currently compete with the much larger scale of the beef industry. Therefore, many bison producers apply cattle husbandry practices and standards to bison. Artificial selection based on husbandry and economics may make good business sense in the short term, but it will not conserve native bison germplasm.


The long term objectives and goals that drive commercial bison production generally differ from the major issues associated with the conservation of the wild species. Furthermore, commercial bison operations could pose a threat to conservation populations through a form of genetic pollution if genetically selected commercial animals are mixed into conservation herds or escape and join wild herds. The most prudent action is to identify and maintain existing conservation herds, and avoid mixing commercially propagated stock into those herds. Bison producers and the bison industry could benefit in the long term by supporting efforts to restore and maintain conservation herds, particularly those subject to a full range of natural selection pressures (Chapter 7). Conservation herds secure the bison genome for the future use of producers—an option not available for most other domestic animals.


26


Chapter 5

Reportable or Notifiable Diseases Lead Authors: Keith Aune, C. Cormack Gates and Delaney Boyd. Contributors: Brett T. Elkin, Martin Hugh-Jones, Damien O. Joly, and John Nishi.

Throughout their range, bison host numerous pathogens and parasites, many of which also occur in domestic cattle (see reviews: Berezowski 2002; Tessaro 1989; Reynolds et al. 2003). In this review, we consider only infective organisms that may negatively affect bison populations, or their conservation, either through direct pathobiological effects, or indirectly as a consequence of management interventions. Livestock diseases that restrict trade or pose a risk to human health may be “reportable” or “notifiable” under federal and provincial/state legislation. In Canada, reportable and immediately notifiable diseases are listed nationally under the authority of the Health of Animals Act and Regulations (http://laws.justice.gc.ca/en/H-3.3/, accessed 15 April 2009) and under provincial statutes and legislation. The Canadian Health of Animals Act requires owners and anyone caring for animals, or having control over animals, to immediately notify the Canadian Food Inspection Agency (CFIA) when they suspect or confirm the presence of a disease prescribed in the Reportable Diseases Regulations. The CFIA reacts by either controlling or eradicating the disease based upon a programme agreed to by stakeholders (CFIA 2001). In the U.S., the U.S. Department of Agriculture Animal and Plant Health Inspection Service (APHIS) conducts federal eradication programmes for several reportable livestock diseases and is involved in a negotiated multi-jurisdictional brucellosis management programme for bison in Yellowstone National Park (YNP) (APHIS, USDA 2007; NPS-USDOI 2000). In both countries, Federal legislation supersedes state and provincial disease control legislation. In the U.S. and Canada there are specific state and provincial regulations that require testing for, and reporting of, various diseases. These regulations may be more extensive than federal requirements, but typically include those diseases regulated by the federal animal health authorities. Much like the U.S and Canada, Mexico has federal animal disease regulations that are administered by the Secretary of Agriculture, Livestock Production, Rural Development, Fishery and Food (SAGARPA). Disease surveillance programmes and zoosanitary requirements, including disease reporting, are established by federal law to protect trade in Mexico and are administered by a decentralised branch of SAGARPA titled the National Service of Health, Safety, and Agricultural Food Quality (SENASICA, see http://www.senasica.gob.mx). SAGARPA

also negotiates bi-lateral disease management agreements for important livestock diseases along the U.S. border, including bovine tuberculosis, brucellosis, and screwworm. In addition to federal, state and provincial regulatory agencies there is an international organisation that influences animal disease reporting in North America. The World Organization for Animal Health (OIE) is an intergovernmental organisation created by international agreement in 1924. In 2008 the OIE had 172 member countries. Every member country is committed to declaring the animal diseases it may detect in its territory. The OIE disseminates this information to help member countries to protect themselves from the spread of disease across international boundaries. The OIE produces sanitary codes with rules that must be observed by member countries to prevent the spread of significant diseases around the world. OIE has established Sanitary Codes for Terrestrial Animals, and the Manual for Diagnostic and Vaccine Tests for Terrestrial Animals, which may influence the international movement of bison (http:// www.oie.int/eng/normes/mcode/en_sommaire.htm). All three countries in North America are members of OIE. Depending on the nature of the disease, management of reportable diseases in captive or commercial herds in North America may involve development and application of uniform protocols to reduce disease prevalence, zoning of management areas by disease status, or imposition of procedures for disease eradication, including test and slaughter, or depopulation. Where reportable diseases are detected, federal, state or provincial legislation affects management of wild bison populations. Interventions may include limiting the geographic distribution of an infected wild population, (e.g., removals at park boundaries to reduce the risk of the disease spreading to adjacent livestock population), quarantine, treatment, or eradication of infected captive conservation breeding herds, or limiting inter-population or inter-jurisdictional transport of bison. Public perception of bison as specific, or non-specific, carriers of diseases is a potential barrier to re-establishing conservation herds, particularly in regions where conventional livestock grazing occurs. National and state/provincial governments may restrict the import/export of bison for conservation projects based on real or perceived risks of infection and transmission of reportable diseases.


5.1

Diseases of Conservation Concern

The American Bison Specialist Group (ABSG) recognises nine federally listed diseases of concern for bison conservation in North America. Regulations applicable to each disease may vary among jurisdictions and in their impact on bison conservation and restoration efforts. The OIE lists seven of these diseases as “notifiable” under international standards.

5.1.1

Anaplasmosis

The etiologic agent of anaplasmosis is Anaplasma marginale, a rickettsia that parasitises the red blood cells of host animals. The organism is transmitted by blood sucking insects, such as ticks, which serve as a vector between hosts (Radostits et al. 2000). The interplay of susceptible wild ruminants and arthropod vectors is critical to the epizootiology of the disease. Anaplasmosis is a disease of international regulatory concern and, therefore, significantly impacts livestock trade between Canada and the north-central and north-western U.S. Anaplasmosis is a disease of major economic importance to the cattle industry in infected regions. Bison are known hosts of A. marginale (Zaug 1986) and wild bison have demonstrated serologic titres for the disease (Taylor et al. 1997). They have also been experimentally infected (Kocan et al. 2004; Zaugg 1986; Zaugg and Kuttler 1985). Serodiagnosis in wild ungulates has proven largely unreliable, but modern molecular diagnostic procedures have provided an excellent alternative (Davidson and Goff 2001). Naturally occurring infections have been reported in the National Bison Range (NBR), Montana, where 15.7% of bison tested positive for anaplasmosis (Zaugg and Kuttler 1985). Recent studies demonstrated A. marginale infection in two widely separated bison herds in the U.S., one in Oklahoma (Nature Conservancy Tallgrass Prairie Preserve) and one in Saskatchewan (De La Fuente et al. 2003). In the Canadian herd, serology and polymerase chain reactions indicated that 10 individuals were infected with A. marginale whereas 42 of 50 bison culled from the Tallgrass Prairie Preserve (TGPP) tested positive serologically as carriers of A. marginale. The U.S. bison isolate of A. marginale was found to be infective when inoculated into susceptible splenectomised calves. Clinical symptoms in bison are similar to those described for cattle. They include anaemia, jaundice, emaciation, and debility (Radostits et al. 2000). Experimentally infected bison calves demonstrated mild clinical signs suggesting that bison may be more resistant than cattle (Zaugg and Kuttler 1985). The disease occurs commonly in Africa, the Middle East, Asia, Australia, the U.S., Central and South America, and southern Europe. If anaplasmosis is diagnosed in Canadian cattle or bison, Canada’s current foreign animal disease strategy calls for its eradication through the testing of infected and exposed herds and the removal of infected individuals. Every bison imported into Canada from 28

the U.S. must be quarantined from the time of its importation into Canada until it proves negative to tests for anaplasmosis performed at least 60 days after it was imported into Canada (CFIA 2007). Programmes for managing this disease in domestic animals include vector control, vaccination and antibiotic therapy (Davidson and Goff 2001). Anaplasmosis is not infectious to humans.

5.1.2

Anthrax

Anthrax is an infectious bacterial disease caused by the endospore-forming bacterium Bacillus anthracis (Dragon and Rennie 1995). After inhalation or ingestion by a susceptible host, B. anthracis endospores germinate and the vegetative form of the bacterium replicates in the bloodstream, releasing toxins that cause septicaemia and death (Dragon and Rennie 1995; Gates et al. 2001b). Upon release from a carcass, highly resistant endospores can remain viable in the soil for decades before infecting a new host (Dragon and Rennie 1995). Humans have played an important role in the evolution of anthrax by increasing the proliferation and dispersal of this global pathogen. Observations of the role of climatic factors, such as season of year, ambient temperature, and drought in promoting anthrax epizootics have been made for several decades (APHIS, USDA 2006). The commonality of summer months, high ambient temperatures, drought, and anthrax epizootics are noncontentious. The roles of environmental factors such as soil types and soil disturbances via excavation are poorly defined despite attempts to evaluate these potential factors. Bacillus anthracis is divided into three genotype branches with distinct geographic sub-lineage compositions that vary regionally around the globe (Van Ert 2007). Van Ert (2007) analysed 273 isolates of B. anthracis in North America, reporting a cosmopolitan assortment of 44 multiple locus, variable number, tandem repeat analysis genotypes. One hypothesis holds that B. anthracis was introduced from the Old World to the New World in spore-infected animal products (wool, skins, bone meal, shaving brushes) transported to the south-eastern seaboard during the European colonial-era (Hanson 1959; Van Ness 1971). Consistent with this hypothesis, Van Ert (2007) found a single dominant sub-group in North American (A.Br. WNA; 70% of genotypes) that is closely related to the dominant European sub-group A.Br.008/009. The diversity of sub-lineages represented varies geographically in North America. A.Br.WNA predominates in the north, while the industrialised south-eastern region of the continent contains a cosmopolitan assortment of less common B. anthracis genotypes in addition to the dominant form A.Br.WNA. The geographic pattern of sub-lineage occurrence in North America is consistent with the hypothesis of an early initial introduction of a limited number of sub-lineages (perhaps


one) followed by its widespread dispersal and ecological establishment. Wild bison were abundant and widely distributed at the time of European colonisation. Once infected with anthrax they may have played an important early role in the ecological establishment and widespread dispersal of A.Br.WNA. The broad diversity of anthrax lineages represented in the industrialised south-eastern region of the continent (Van Ert et al. 2007) is suggestive of the accumulation of additional sub-group types over time. A likely mechanism is importation of contaminated animal products into mills and tanneries on the eastern seaboard and New England which process imported hair, wool, and hides. The World Health Organisation (WHO 2008) commented on the role of tanneries as a point source of anthrax outbreaks. Contaminated products come from animals that died of anthrax. Wastewater effluent from plants can contaminate downstream sediments and pastures with anthrax spores, providing a source of local outbreaks in livestock and further proliferation of novel introduced variants of the pathogen. Marketing of inadequately sterilised bone meals and fertilisers, rendered from contaminated materials, can result in long distance redistribution and introducing “industrial” strains to livestock remote from the original source (Hugh-Jones and Hussaini 1975). Under certain environmental conditions, concentrations of endospores have caused periodic outbreaks among wood bison in the Slave River Lowlands (SRL), Mackenzie Bison Sanctuary (MBS), and Wood Buffalo National Park (WBNP) (Dragon and Elkin 2001; Gates et al. 2001b; Pybus 2000). Between 1962 and 1971, anthrax and the associated depopulation and vaccination programmes employed to control the disease, accounted for over 2,800 wood bison deaths (Dragon and Elkin 2001). Further outbreaks occurred in the MBS in 1993, in the SRL in 1978, 2000 and 2006, and in WBNP in 1978, 1991, 2000, and 2001 (Gates et al. 1995; Nishi et al. 2002c). Four factors that are associated rather consistently with these epizootics are high ambient temperatures, intense mating activity, high densities of insects, and high densities of bison as they congregate and compete for diminishing water and food supplies (APHIS, USDA 2006). Based on these four factors, two hypotheses have been proposed to explain outbreaks of anthrax in bison in northern Canada: (1) “the modified host resistance hypothesis” (Gainer and Saunders 1989) and (2) “the wallow concentrator hypothesis” (Dragon et al., 1999). These two hypotheses are not mutually exclusive. A recent outbreak was reported in a commercial herd in south-western Montana that killed over 300 bison pasturing on a large foothills landscape beneath the Gallatin Mountain Range (Ronnow 2008). Despite mass deaths of bison during anthrax outbreaks, the sporadic nature of outbreaks and predominance of male deaths suggest that the disease plays a minor role in long-term population dynamics unless operating in conjunction with other limiting factors (Joly and Messier 2001b; Shaw and Meagher 2000). Anthrax is not treatable in

free-ranging wildlife, but captive bison can be vaccinated or treated with antibiotics (Gates et al. 1995; Gates et al. 2001b). Carcass scavenging facilitates environmental contamination with anthrax spores (Dragon et al. 2005); therefore timely carcass treatment and disposal during an active outbreak in free-ranging bison is considered an important preventative strategy for reducing the potential for future outbreaks (HughJones and de Vos 2002; Nishi et al. 2002a). Anthrax is a public health concern and humans are susceptible, however, exposure from naturally occurring outbreaks requires close contact with animal carcasses or hides. In addition, humans have rarely been exposed to anthrax through the purchase of curios purchased by tourists (Whitford 1979).

5.1.3

Bluetongue

Bluetongue (BLU) is an insect-borne viral hemorrhagic disease affecting many ungulates in the lower latitudes of North America. The BLU virus is a member of the genus Oribivirus of the family Reoviridae. Worldwide there are 24 known BLU serotypes, but only six are active in domestic and wild ruminants from North America (Pearson et al. 1992). Bluetongue viruses are closely related to the viruses in the epizootic hemorrhagic disease and BLU is known to infect a wide variety of wild and domestic ruminants (Howerth et al. 2001). Bison are susceptible to BLU, and the virus has been isolated under field, captive, and experimental conditions (Dulac et al. 1988). The arthropod vectors of the bluetongue virus are various species of Culicoides midges (Gibbs and Greiner 1989; Howerth et al. 2001). Clinical symptoms include fever, stomatitis, oral ulcerations, lameness, and occasionally, reproductive failure (Howerth et al. 2001). There are subacute, acute, and even chronic expressions of the disease in many wild ungulates and domestic livestock. BLU typically occurs in the late summer and early fall depending upon the seasonal patterns of vector activity (Howerth et al. 2001). Factors influencing the frequency and intensity of disease outbreaks are innate herd immunity, virulence factors associated with viruses, and vector competency and activity. BLU occurs in livestock over much of the U.S. and its distribution parallels that of domestic livestock. Its distribution is more limited in Canada where it once was a regulated disease until rules were relaxed in July 2006 (CFIA website). There is considerable difference in the epidemiology of the disease between northern and southern portions of North America depending on the consistency of vector activity. In the southern areas, vector activity is more common and animal populations exhibit a higher prevalence of seroreactivity and antibody protection. BLU has not been widely reported in bison herds in North America. Serologic surveys of several Department of Interior bison herds in the U.S. have not found seroreactors for bluetongue virus (T. Roffe personal communication; Taylor et al. 1997). The U.S. Fish and Wildlife Service (USFWS) has opportunistically examined bison


near a recent outbreak of BLU in deer and found no evidence of exposure (T. Roffe personal communication). As with many vector-born diseases, climate change is a potential factor affecting the distribution of vectors and therefore the occurrence of BLU (Gibb 1992). There is no effective treatment and, under natural conditions, the disease is not considered a significant threat to human health. There has been one human infection documented in a laboratory worker (WHO website).

5.1.4

Bovine spongiform encephalopathy

Bovine spongiform encephalopathy (BSE), or “mad cow disease” as it is commonly known, is one of a suite of distinct transmissible spongiform encephalopathies (TSE) identified during the past 50 years. TSEs are apparently caused by rogue, misfolded protein agents called prions (PrPSC) that are devoid of nucleic acids (Prusiner 1982). No other TSE in man or animal has received more worldwide attention than BSE (Hadlow 1999). It was first identified in 1986 in England and has since had far reaching economic, political, and public health implications. BSE is a neurologic disease characterised by spongiform change in gray matter neurophil, neuronal degeneration, astrocytosis, and accumulation of misfolded PrPSC (Williams et al. 2001). Clinically the disease is progressive, displaying gradual neurologic impairment over months or years and is usually fatal. The disease causes progressive weight loss, low-level tremors, behavioural changes, ataxia, and postural abnormalities. Substantial evidence exists for genetic variation in susceptibility among and within species (Williams et al. 2001). Cases of BSE were identified in 10 species of Bovidae and Felidae at a zoological collection in the British Isles (Kirkwood and Cunningham 1994). At least one of these cases included bison. Worldwide, other species susceptible to BSE include cheetah, macaques and lemurs (Williams et al. 2001). The recent BSE epidemic in Europe was linked to oral ingestion of contaminated feed (containing ruminant derived protein), however, there is some evidence for low-level lateral transmission. There are no known treatments or preventions for BSE. The human form called new variant Creutzfeldt-Jakob disease has been linked to consumption of BSE contaminated foods. Due to the risk of human exposure to BSE, this disease is highly regulated worldwide. Recent cases of BSE have been reported in Canada and the U.S. but are extremely rare in the livestock industry. Canada reported a case in 1993 that was imported from England and the first domestic case was detected in 2003. The U.S. reported its first case of BSE in 2003. Since then, protein byproducts were banned in livestock feed, national surveillance was implemented in both countries, and several regulations were promulgated to restrict imports and exports across the U.S.-Canada boundary. Although bison are considered to be susceptible, there has not been a case of BSE reported in American bison. 30

5.1.5

Bovine brucellosis

Bovine brucellosis, also known as Bang’s disease, is caused by infection with the bacterium Brucella abortus (Tessaro 1989; Tessaro 1992). The primary hosts for bovine brucellosis are cattle, bison, and other bovid species (Tessaro 1992), however, other wild ungulates such as elk (Cervus elaphus) are also susceptible and seem to play a role in interspecies transmission in the Greater Yellowstone Area (GYA) (Davis 1990; Rhyan et al. 1997; Thorne et al. 1978). Evidence suggests that brucellosis was introduced to North America from Europe during the 1500s (Meagher and Mayer 1994; Aguirre and Starkey 1994). The disease is primarily transmitted through oral contact with aborted foetuses, contaminated placentas, and uterine discharges (Reynolds et al. 1982; Tessaro 1989). The impacts of brucellosis on female bison include abortion, inflammation of the uterus, and retained placenta (Tessaro 1989). Greater than 90% of infected female bison abort during the first pregnancy; however, naturally acquired immunity reduces this abortion rate to 20% after the second pregnancy, and to nearly zero after the third pregnancy (Davis et al. 1990; Davis et al. 1991). Male bison experience inflammation of the seminal vessels, testicles, and epididymis, and, in advanced cases, sterility (Tessaro 1992). Both sexes are susceptible to bursitis and arthritis caused by concentrations of the bacterial organism in the joints, resulting in lameness, and possibly increased vulnerability to predation (Tessaro 1989; Tessaro 1992). Serology is used to detect exposure to B. abortus by identifying the presence of antibodies in the blood. Sero-prevalence is the percentage of animals in a herd that carry antibodies (Cheville et al. 1998). A sero-positive result, indicating the presence of antibodies, does not imply current infection, and may overestimate the true level of brucellosis infection (Cheville et al. 1998; Dobson and Meagher 1996) because the organism must be cultured from tissue samples to diagnose an animal as infected. However, a disparity between serology results and level of infection could also be attributed to false negative culture results related to the difficulties in isolating bacteria from chronically infected animals (Cheville et al. 1998). There is currently no highly effective vaccine for preventing bovine brucellosis (Cheville et al. 1998; Davis 1993). Strain 19 (S19) was a commonly used vaccine administered to cattle from the 1930s until 1996 (Cheville et al. 1998). It was only 67% effective in preventing infection and abortion in cattle (Cheville et al. 1998). S19 was found to induce a high frequency of abortions in pregnant bison (Davis et al. 1991). Other studies failed to demonstrate efficacy of S19 as a bison calfhood vaccine (Templeton et al. 1998). A newer vaccine, strain RB51, is now preferred over S19 because it does not induce antibodies that can interfere with brucellosis serology tests for disease exposure (Cheville et al. 1998; Roffe et al. 1999a). RB51 protects


cattle at similar levels to S19 (Cheville et al. 1993). Doses of RB51 considered to be safe in cattle were found to induce endometritis, placentitis, and abortion in adult bison (Palmer et al. 1996). However, Roffe et al. (1999a) found RB51 had no significant adverse effects on bison calves. The safety and efficacy of RB51 in bison remains unclear but, nonetheless, it was provisionally approved for use in bison in the U.S. The vaccine is not recognised in Canada and vaccinated cattle are not allowed into the country (CFIA 2007). Every bison imported into Canada from the U.S. must be quarantined from the time of its importation into Canada until it proves negative to tests for brucellosis performed not less than 60 days after it was imported into Canada (CFIA 2007). Quarantine protocols have been developed for bison to progressively eliminate all animals exposed to brucellosis from a population (APHIS, USDA 2003; Nishi et al. 2002b). These protocols have been successful for eliminating brucellosis in wood bison through the Hook Lake project and are currently being attempted in the GYA (Aune and Linfield 2005; Nishi et al. 2002b). Results from these two studies, and other case studies (HMSP, WCNP and EINP), have shown that brucellosis can be effectively eliminated from exposed populations with a high degree of certainty using test and slaughter protocols.

5.1.6

Bovine tuberculosis

Bovine tuberculosis (BTB) is a chronic infectious disease caused by the bacterium Mycobacterium bovis (Tessaro et al. 1990). The primary hosts for BTB are cattle and other bovid species, such as bison, water buffalo (Bubalus bubalis), African buffalo (Syncerus caffer), and yak (Bos grunniens). Primary hosts are those species that are susceptible to infection and will maintain and propagate a disease indefinitely under natural conditions (Tessaro 1992). Other animals may contract a disease, but not perpetuate it under natural conditions; these species are secondary hosts. The bison is the only native species of wildlife in North America that can act as a true primary host for M. bovis (Tessaro 1992). Historical evidence indicates that BTB did not occur in bison prior to contact with infected domestic cattle (Tessaro 1992). Currently, the disease is only endemic in bison populations in and near WBNP, where it was introduced with translocated plains bison during the 1920s. BTB is primarily transmitted by inhalation and ingestion (Tessaro et al. 1990); the bacterium may also pass from mother to offspring via the placental connection, or through contaminated milk (FEARO 1990; Tessaro 1992). The disease can affect the respiratory, digestive, urinary, nervous, skeletal, and reproductive systems (FEARO 1990; Tessaro et al. 1990). Once in the blood or lymph systems the bacterium may spread to any part of the host and establish chronic granulomatous lesions, which may become caseous, calcified, or necrotic (Radostits et al. 1994; Tessaro 1992). This chronic disease is progressively debilitating to the

host, and may cause reduced fertility and weakness; advanced cases are fatal (FEARO 1990). The disease manifests similarly in cattle and bison (Tessaro 1989; Tessaro et al. 1990). Both the U.S. and Canada perform nationwide surveillance of abattoir facilities to monitor BTB infection in cattle and domestic bison. There is no suitable vaccine available for BTB (FEARO 1990; CFIA 2000; APHIS USDA 2007). Every bison imported into Canada from the U.S. must be quarantined from the time of its importation into Canada until it proves negative to tests for BTB performed at least 60 days after it was imported into Canada (CFIA 2007). A quarantine protocol has been developed and an experimental project was attempted to salvage bison from a BTB exposed population (Nishi et al. 2002b). Although at first it appeared to be a successful tool for salvaging bison from an exposed herd, after 10 years, several of the salvaged animals expressed BTB, and in 2006 all salvaged animals were slaughtered (Nishi personal communication). There is some evidence that BTB can be treated in individual animals using long term dosing with antibiotics, but the duration of treatment, costs of therapy, and the need for containment make this option impractical for wildlife. The only definitive method for completely removing BTB from a herd is depopulation (CFIA 2000; APHIS USDA 2005). The only alternative to depopulation is controlling the spatial distribution and prevalence of disease through a cooperative risk management approach involving all stakeholders. The basic prerequisites for effectively addressing risk management associated with BBTB in bison are teamwork, collaboration across professional disciplines, and respect for scientific and traditional ecological knowledge among technical and non technical stakeholders (Nishi et al. 2006). BTB can infect humans, but it is treatable with antimicrobial drugs. Human TB due to M. bovis has become very rare in countries with pasteurised milk and BTB eradication programmes.

5.1.7

Bovine viral diarrhoea

Bovine viral diarrhoea (BVD) is a pestivirus that infects a wide variety of ungulates (Loken 1995; Nettleston 1990). Serologic surveys in free-ranging and captive populations demonstrate prior exposure in more than 40 mammal species in North America (Nettleston 1990; Taylor et al. 1997). The suspected source of BVD in wild animals is direct contact with domestic livestock. Infections in wild ruminants, like cattle, are dependent upon the virulence of the isolate, immune status of the animal host, and the route of transmission. Infections in cattle are usually subclinical, but some infections may cause death or abortions in pregnant animals. Factors influencing the persistence of BVD include population size and density, herd behaviour, timing of reproduction, and survivorship of young (Campen et al. 2001). Positive serologic evidence was reported for blood samples from bison in the GYA (Taylor et al. 1997; Williams et al. 1993),


Alaska (Zarnke 1993) and from bison at Elk Island National Park (EINP) in Alberta (Cool 1999; Gates et al. 2001b). In YNP, positive antibody titres were detected in 31% of tested animals (Taylor et al. 1997). There are unpublished data regarding seroreactivity from bison transported to Montana from WCNP in South Dakota (K. Kunkel, personal communication). The Jackson bison herd, with a known history of commingling with cattle, has demonstrated low-level titres, but no evidence of BVD antigen or clinical disease has been found (T. Roffe, personal communication). Clinical BVD was reported in the EINP plains bison herd in 1996, prompting a serological survey of plains bison and wood bison herds (Cool 1999; Gates et al. 2001b). Forty-seven percent of 561 plains bison from EINP tested seropositive for BVD; one tested positive for the virus antigen. At least six plains bison deaths in EINP were attributed to the BVD virus (Cool 1999). Tissues from the suspected cases of BVD infected plains bison were submitted to the Animal Disease Research Institute, Lethbridge, Alberta, Canada, and type 1 BVD virus was isolated (Tessaro and Deregt 1999). None of 352 wood bison in the Park tested sero-positive for BVD at the time. Both plains and wood bison populations at EINP are vaccinated for BVD during annual roundups. However, calves used in translocations are not vaccinated to allow future screening of recipient populations for BVD. In Poland, Sosnowski (1977) reported BVD in a captive European bison. BVD is common in cattle in North America and poses no known risk to humans.

5.1.8

Johne’s disease

Johne’s disease (JD) is caused by the etiologic agent Mycobacterium avium subsp. paratuberculosis, a hardy bacterium related to the agents of leprosy and tuberculosis. It occurs worldwide affecting a variety of domestic and wild ruminants including bison, cattle, and sheep (Buergelt et al. 2000; Williams 2001). Infections often lead to chronic granulomatous enteritis with clinical signs of diarrhoea, weight loss, decreased milk production, and mortality. JD is common in cattle. Recent studies have shown that more than 20% of dairy herds in the U.S. have JD (Chi et al. 2002; Ott et al. 1999) causing an estimated economic loss of more than US$200 million annually. JD typically enters a herd when infected, asymptomatic animals are introduced. Unpasteurised raw milk or colostrum may be a source of infection for artificially raised calves. Animals are most susceptible to infection during their first year of life. Neonates most often become infected by swallowing small amounts of contaminated manure from the ground or from their mother’s udder. Animals exposed to a very small dose of bacteria at a young age, and older animals, are not likely to develop clinical disease until they are much older. After several years, infected animals may become patent and shed mycobacteria in their faeces. Typically, pre-patent animals do not show symptoms of disease; consequently, most 32

infections go unnoticed and undiagnosed. There is no treatment for animals infected with JD and prevention is the best control measure. Humans are not considered susceptible, but M. a. paratuberculosis has been isolated in patients with chronic enteritis (Crohn’s disease) (Chiodini 1989). JD is not considered to be a disease problem when bison are on open rangelands and managed at low density. However, restrictions may apply to inter-jurisdictional movement of animals from known infected herds. Hence, maintaining low risk status for bison herds used as a source for conservation projects is an important consideration. In 1998, the U.S. Animal Health Association approved the Voluntary Johne’s Disease Herd Status Program for cattle (VJDHSP). The VJDHSP provides testing guidelines for States to use to identify livestock herds as low risk for JD infection. With numerous tests over several years, herds progress to higher status levels. The higher the status level, the more likely it is that a herd is not infected with JD. In April 2002, USDA-APHIS-Veterinary Service incorporated portions of this programme into national programme standards: Uniform Program Standards for the Voluntary Bovine Johne’s Disease Control Program (VBJDCP). VBJDCP-test-negative herds serve as a source of low JD risk stock. Testing for JD in conservation herds has been sporadic and opportunistic. Diagnostic tools are being developed and improved. There are no reports of JD in conservation bison herds in the literature, however, some commercial operations have discovered JD, and in many cases are managing to prevent its spread and reduce its impact on the industry.

5.1.9

Malignant catarrhal fever (sheep associated)

Malignant catarrhal fever (MCF) is a serious, often fatal disease affecting many species of the Order Artiodactyla. It is caused by viruses of the genus Rhadinovirus. At least 10 MCF viruses have been recognised worldwide and five viruses have been linked to disease. The viruses most significant to livestock are those carried by sheep, goats or wildebeest (Connochaetes spp.). Although ovine herpes virus type 2 (sheep associated MCF) does not cause disease in its natural host, domestic sheep, it does cause MCF in bison. Serological testing indicated that it is common in domestic goats (61%) and sheep (53%) in the U.S. (Li et al. 1996). MCF is an important disease in the commercial bison industry as it is one of the most infectious diseases of bison, especially at high densities (Heuschele and Reid 2001). It causes highly lethal infections in bison, with the reported incidence of mortality in a herd of up to 100% (Schultheiss et al. 2001). Infections proceed rapidly to clinical disease. MCF is expressed in two forms, acute and chronic, but regardless, death ensues in most cases. In the acute form, bison usually die within 7–10 days of infection or within 48 hr of becoming symptomatic. Alternatively, death may ensue as


long as 156 days post-infection. Some animals recover and remain persistently infected (Schultheiss et al. 1998). Clinical signs in bison include hemorrhagic cystitis, colitis, conjunctivitis, ocular discharge, nasal discharge, excess salivation, anorexia, diarrhoea, melaena, haematuria, multifocal ulceration of the oral mucosa, fever, circling, ataxia, behaviours suggestive of blindness, lameness, and difficult urination (Liggitt et al. 1980; Ruth et al. 1977; Schultheiss et al. 1998). Lymphadenomegaly and corneal opacity occur in fewer than half the cases (Schultheiss et al. 2001). Direct contact between bison and domestic sheep is considered the most likely source of infection. Hence, bison should not be grazed in the same pastures or adjacent to pastures with sheep. Although most infections occur when bison are in close association with domestic sheep, MCF was reported in bison herds that were five kilometres (three miles) from a lamb feedlot (Schultheiss et al. 2001). Dr. T. Roffe has conducted serologic surveys of two U.S. Department of the Interior bison herds not associated with domestic sheep and has found no sero-reactors for MCF (T. Roffe, personal communication). There is no vaccine or effective treatment for MCF and the best way to control this disease is to minimise contact with reservoir hosts. There is no evidence that isolates of MCF are infectious to humans (Heuschele and Seal 1992).

5.2

Episodes of Reportable Diseases in Plains Bison

Based on this survey, two plains bison conservation herds in North America have significant chronic disease issues: YNP herd and the Jackson herd in GTNP/NER. These herds, which account for 4,700 bison (as of winter 2008), or 24% of the entire North American plains bison conservation population, harbour brucellosis.

5.2.1

Yellowstone National Park

Brucellosis was first detected in the YNP bison population in 1917 (Mohler 1917). The origin of brucellosis in the park is unclear, but was probably the result of transmission from cattle (Meagher and Mayer 1994). Opportunistic and systematic serological surveys in the area revealed sero-prevalence varying between 20% and 70%, while bacterial cultures indicated an infection prevalence of approximately 10% (Dobson and Meagher 1996; Meagher and Mayer 1994). Although the true prevalence of the disease is unknown, the YNP bison population is considered to be chronically infected with brucellosis (Cheville et al. 1998). More recent research on the epidemiology of brucellosis in Yellowstone bison found that 46% of the seroreactor animals were culture positive (Roffe et al. 1999b). Recent demographic analysis indicates that brucellosis has a significant reproductive effect, that the growth rate of the population could increase by 29% in the absence of brucellosis (Fuller et al. 2007),

and that brucellosis is not a threat to the long-term viability of the YNP bison (Mayer and Meagher 1995; USDOI and USDA 2000). Fuller et al. (2007) conducted a detailed analysis of the demographics of the Yellowstone population from 1900-2000 and found evidence of density dependent changes in population growth as numbers approached 3,000 animals. This population appears robust and has grown at times to exceed 4,000, although it was reduced to fewer than 3,000 several times during the past decade under the current herd management regime (R. Wallen, personal communication). Herd management is affected by the presence of brucellosis primarily because of the potential risk the disease poses to the livestock industry (Keiter 1997). Bison leaving the park could potentially transmit the disease to domestic cattle grazing on adjacent National Forest and private lands in Montana, Wyoming or Idaho (USDOI and USDA 2000). Bison leave the park in the winter on the north and west boundaries within Montana; movement to the east and south is rare because of topographical barriers (R. Wallen, personal communication). Transmission of brucellosis from bison to cattle has been demonstrated in captive studies; however, there are no confirmed cases of transmission in the wild (Bienen 2002; Cheville et al. 1998; Shaw and Meagher 2000). Nevertheless, the potential exists, and this has created a contentious bison management issue in the area. Relying on the Animal Industry Act of 1884, the U.S Department of Agriculture began preventing and controlling the spread of contagious livestock diseases in the U.S. In 1947, federal and state officials began working closely with the livestock industry to eradicate brucellosis (Keiter 1997; NPS USDOI 2000). Each state represented in the GYA is a co-operator in the National Brucellosis Program and has authority to implement control programmes for brucellosis infected or exposed animals within their respective boundaries. Due to the transmission of brucellosis to cattle, presumably by elk, Montana, Wyoming, and Idaho have each periodically lost their brucellosis-free status as certified by APHIS. Transmission of brucellosis to cattle in Montana, Wyoming or Idaho indirectly affects all producers in these states. If their APHIS status is downgraded, other states may refuse to accept cattle from producers in the GYA (Cheville et al. 1998). Resolution of this issue requires the involvement of, and cooperation among, agencies in several jurisdictions: The National Park Service (NPS), the U.S. Forest Service (USFS), APHIS, and the State of Montana Department of Livestock (MDOL) and Montana Department of Fish, Wildlife, and Parks (MFWP). After many years of media and legal controversy over bison management, the agencies acknowledged the need to cooperatively develop a long-term bison management plan (Plumb and Aune 2002). In 1990, they commenced the process


for an interagency environmental impact statement to develop alternatives for the plan (USDOI and USDA 2000). A series of interagency interim plans followed, which progressively incorporated greater tolerance for bison outside the park in certain areas, and enabled NPS and MFWP personnel to lethally remove bison moving from YNP into Montana. Legal and policy disagreements between the federal agencies and the State of Montana inhibited the development of a longterm interagency management plan until 2000 when courtordered mediation resulted in a final decision for a long-term management approach. The long-term plan employs an adaptive management approach with three phased steps for each of the north and west boundary areas (USDOI and USDA 2000). The plan incorporates several risk management strategies including spatial and temporal separation of bison and cattle, capture, test, and slaughter of sero-positive bison, hazing of bison back into the park, vaccination, and radio-telemetry monitoring of pregnant bison to locate possible sources of infection if a cow gives birth or aborts outside the park (USDOI and USDA 2000). The ultimate purpose of the plan is to maintain a wild, freeranging population of bison while, at the same time, protecting the economic viability of the livestock industry in Montana by addressing the risk of brucellosis transmission; it is not a brucellosis eradication plan (Plumb and Aune 2002). Although eradication of brucellosis from bison in the park is a possible future goal, such an effort is complicated by retransmission potential from elk in the GYA, which also harbour the disease (Cheville et al. 1998). Development of more effective vaccines and vaccination methods for bison and elk are required before considering eradication alternatives (Cheville et al. 1998). Recent research on genes that control natural resistance to brucellosis may also provide future methods for eradicating brucellosis (Templeton et al. 1998). Recent transmission of brucellosis from elk to cattle and the subsequent loss of Montana’s brucellosis status have complicated management. Current initiatives are aimed at managing the problem of brucellosis in elk and bison. Changes in the distribution of bison, elk, and cattle will generate further public debate and perhaps legal action. The GYA situation illustrates the tremendous difficulty in managing wild free ranging ungulates affected by a significant disease on a large landscape where human livelihoods are at risk.

5.2.2

Grand Teton National Park/National Elk Refuge (Jackson herd)

The Jackson herd of approximately 1,100 animals resides in the southern end of the GYA (USFWS and NPS 2007), migrating between Grand Teton National Park (GTNP) in the summer and the adjacent National Elk Refuge (NER) in the winter (Cheville et al. 1998). As with the YNP herd, the Jackson herd is chronically 34

infected with brucellosis. Williams et al. (1993) reported seroprevalence of 77% and infection prevalence of 36% for the herd. Serology tests over the past five years indicate a sero-prevalence of 80% (S. Cain, personal communication). A reduction of 8% in fecundity has been estimated, however, the population has been increasing since the 1970s despite the disease (S. Cain, personal communication, Chapter 6; USFWS-NPS 2007). The Jackson herd was founded in 1948 with the reintroduction of 20 bison from YNP to a 1,500-acre display pen. These bison were confined until 1963 when brucellosis was discovered in the herd (Cheville et al. 1998). All but four vaccinated yearlings and five vaccinated calves were destroyed. In 1964, Theodore Roosevelt National Park (TRNP) provided 12 brucellosis-free bison to augment the Jackson herd (Cheville et al. 1998). In 1968, the herd escaped from the progressively deteriorating enclosure facility (Cheville et al. 1998; Williams et al. 1993). From that point the park allowed the herd to roam freely. The bison herd discovered the feed ground at the NER in 1980. Although the herd was apparently healthy when released, it is suspected that infected elk on the NER introduced brucellosis to the Jackson bison (Cheville et al. 1998). Similar to the YNP herd, the free-ranging nature of the Jackson herd allows for the possibility of transmitting brucellosis to domestic livestock in the area, although since the NER excludes cattle, there is limited contact between Jackson bison and cattle during the winter feeding period (Cheville et al. 1998). There is potential for contact, however, when bison move among private, USFS, GTNP and NER jurisdictions, especially in summer, when cattle are maintained on grazing allotments in GTNP, private ranchlands, and adjacent USFS lands (Cheville et al. 1998; Keiter 1997). A new bison and elk management plan for the NER and GTNP was approved in April 2007. An earlier bison management plan approved in 1996, after undergoing a National Environmental Policy Act (NEPA) process, was subject to litigation by an animal rights group that questioned the inclusion of a sport hunt to manage population levels and the exclusion of an analysis of elk management on the federal lands in the decision process (Cain, personal communication; USFWS-NPS 2001). The court ruled that destruction of bison for population control could not be conducted until the involved agencies analysed the effects of winter feeding on bison and elk through an additional NEPA process (USFWS-NPS 2001). The feeding grounds attract 90% of the Jackson bison and 6,000-8,000 elk to one small area, creating zones of high animal density, where transmission may be enhanced among and between elk and bison (Bienen 2002; USFWS-NPS 2007). GTNP and the NER determined that a combined elk and bison management plan is needed to address the interconnected issues of the two species, including winter feeding and disease management. The Jackson bison


and elk herds migrate across several jurisdictions including the NER, GTNP, YNP, Bridger-Teton National Forest, Bureau of Land Management, State of Wyoming, and private lands. The NPS and FWS coordinated the extensive involvement of the associated agencies, organisations, and private interests affected by this new management plan and Environmental Impact Statement (EIS). The U.S. Department of Interior (USDOI) published a record of decision in April 2007, selecting a management alternative that emphasises adaptive management of elk and bison populations while reducing their dependence upon feed grounds. The plan also calls for a brucellosis vaccination programme for elk and bison conducted by the State of Wyoming. Recent hunting programmes, modification of feeding programmes and disease management have reduced the number of bison to 700 animals and the long-term management of this herd is now prescribed in a long-term plan. Several legal challenges were mounted and the implementation of the plan remains controversial.

5.3

An Occurrence of Reportable Diseases in Wood Bison

Wood bison herds in and around WBNP, including SRL, are infected with BTB and brucellosis (Gates et al. 1992; Gates et al. 2001c). These diseased herds account for about 50% of the total wood bison conservation population. Joly and Messier (2001a) reported the sero-prevalence of the diseases to be 31% for brucellosis and 49% for tuberculosis. With the exception of free-ranging bison in the WBNP and GYA, aggressive eradication programmes in both the U.S. and Canada have reduced the probability of brucellosis and BTB in domestic cattle and bison herds to extremely low levels. The wild diseased wood bison herds in and near WBNP are the only known reservoirs of BTB among all bison conservation herds (Gates et al. 2001c; Reynolds et al. 2003; Shaw and Meagher 2000). BTB and brucellosis were likely introduced to wood bison populations with the transfer of plains bison from Wainwright Buffalo Park in the 1920s (Fuller 2002). In 1925, the Canadian government implemented a plan to move 6,673 plains bison from the overcrowded Wainwright Buffalo Park to WBNP. The transfer proceeded despite opposition from mammalogical and biological societies in the U.S. and Canada, who warned of transmission of BTB to the resident wood bison population (Anonymous 1925; Ogilvie 1979). BTB was first reported in WBNP in 1937 (Fuller 2002; Gates et al. 1992; Geist 1996). Although it is not known whether BTB was endemic among wood bison prior to the transfer (Reynolds et al. 1982), evidence indicates that the disease was introduced to wood bison with the transfer of plains bison (Fuller 1962). Brucellosis was also present in the plains bison herd and was reported in WBNP in 1956 (Gates et al. 1992).

The presence of BTB and brucellosis threatens the recovery of wood bison in several ways. First, the infected animals are subject to increased mortality, reduced fecundity, and increased vulnerability to predation (Gates et al. 1992; Joly and Messier 2001a). In 1934, the bison population in WBNP was estimated at 12,000 animals (Soper 1941). The population decreased from approximately 11,000 in 1970 to 2,151 in 1999 (Joly 2001). This decrease has been attributed to the interactive effects of diseases and predation (Carbyn et al. 1998; Fuller 1991; Joly and Messier 2001a). Recently, the WBNP population increased to 4,050, although the reasons for this increase are unclear (Bradley 2002, personal communication). Second, the potential exists for the infected herds to transmit the diseases to healthy herds, most notably the Mackenzie, Nahanni, and Hay-Zama herds (Animal Plant and Food Risk Assessment Network (APFRAN 1999). Since 1987, the Government of the Northwest Territories has managed a 39,000 km2 Bison Control Area south of the Mackenzie River to prevent movement of diseased bison into the MBS (Nishi 2002). Recent analysis and modelling of bison movements on the landscape have demonstrated considerable risk potential for transmission of diseases to healthy wood bison herds and bison ranches in the vicinity of the diseased herds (Gates et al. 2001a; Mitchell 2002). The Government of Alberta announced a new hunting season for the Hay Zama herd in 2008. The purpose of the hunt is to maintain the wood bison population at approximately 400 and limit distribution of these animals until the diseased bison issue, in and around WBNP, is successfully resolved. In particular the hunt will be used to control expansion of the Hay-Zama herd eastward, preventing contact with bison emigrating from WBNP that may be infected with brucellosis or BTB. Although preliminary, results of serological tests and post mortem examination of about 100 bison harvested from the Hay-Zama population in the winter of 2008 were negative for the two bovine diseases (D. Moyles, Alberta Sustainable Resource Development, personal communication). Much research and debate has been focused on trying to resolve the diseased bison issue in northern Canada. In 1990, the Federal Environmental Assessment Panel released its report on its analysis of the disease issues (FEARO 1990). The panel concluded that eradication of the diseased wood bison populations is the only method for eliminating the risk of transmission of brucellosis and BTB from bison to domestic cattle, non-diseased wood bison, and humans. The panel further recommended that healthy wood bison be reintroduced to the area following depopulation of the diseased herds. Sources of healthy bison for reintroduction could include the EINP wood bison herd and other captive herds supplemented by diseasefree animals salvaged from the Northern Bison herds (FEARO 1990). One such salvage operation, the Hook Lake Wood Bison Recovery Project in Fort Resolution, Northwest Territories, was


attempted (Nishi et al. 2002b), but failed. In 2006, after 10 years of isolation and rigorous disease testing, BTB-infected bison were detected in the herd. Several constituencies rejected the FEARO (1990) panel’s recommendation to depopulate WBNP herds. The Northern Buffalo Management Board (NBMB) was formed to develop a feasible eradication plan (Chisholm et al. 1998; Gates et al. 1992). The NBMB recommended further research into bison and disease ecology before planning management actions for the region (RAC 2001). In 1995, the Minister of Canadian Heritage formed the Bison Research and Containment Program (BRCP) to focus on disease containment and ecological and traditional knowledge research (RAC 2001). The Minister then created the Research Advisory Committee (RAC) to coordinate research activities under the BRCP (Chisholm et al. 1998). The RAC comprised a senior scientist appointed by Parks Canada, representatives from the Alberta and Northwest Territories governments, Canadian Parks and Wilderness Society, and four aboriginal communities (Chisholm et al. 1998). During the mandated five year period (1996-2001), the BRCP funded projects to assess the prevalence and effects of the diseases on northern bison (Joly and Messier 2001a), and to investigate bison movements and the risk of disease transfer (Gates et al. 2001a). The RAC produced a future research agenda and budget for minimum research still required under the BRCP mandate (RAC 2001), but the programme was discontinued in 2001. Many of the research needs identified by the RAC align with the recommendations outlined in the National Recovery Plan for Wood Bison prepared by the Wood Bison Recovery Team (Gates et al. 2001c). There remains considerable disagreement between federal and provincial governments and aboriginal interests concerning a long-term solution to the WBNP disease issue. Provincial governments support disease eradication, including aggressive intervention to achieve disease eradication within the national park. Parks Canada is concerned about the conservation and biological impacts associated with aggressive intervention. A technical workshop was convened in 2005 to explore the feasibility of removing diseased bison from the Greater Wood Buffalo National Park region followed by a reintroduction of healthy bison (Shury et al. 2006), and there was unanimous agreement amongst participants that this option was technically feasible. The only subsequent management action undertaken at the time of writing was the implementation of a hunting season for the Hay-Zama herd in 2008-2009, intended, in part, to test disease status and to reduce the risk of infection with BTB and brucellosis by reducing population size and limiting range expansion towards infected populations (George Hamilton, Alberta Sustainable Resource Development, personal communication).

36

5.4

Disease Management in Perspective

A primary consideration regarding disease management in wild populations is determining when a disease is a conservation problem and whether intervention is warranted (Gilmour and Munro 1991). It can be argued that parasitism by disease organisms is a crucial ecological and evolutionary force in natural systems (Aguirre et al. 1995; Wobeser 2002). Classification of a pathogen as indigenous or exotic to a host species or ecosystem can influence whether a disease should be managed (Aguirre and Starkey 1994; Aguirre et al. 1995; National Park Service 2000). BTB and brucellosis are believed to have been transmitted to bison from domestic cattle. Therefore, management of these diseases in bison is warranted based on their exotic origins, as well as the threat they pose to domestic animals. However, many other pathogens have coevolved with bison and do not warrant veterinary intervention and should be managed in accordance with a natural system. The most significant diseases involving bison as wildlife affect a trinity of players (wildlife, humans, and domestic animals), and involve a tangle of transmission routes (Fischer 2008). Management of wildlife diseases has often been undertaken to minimise risks to humans and domestic animals (Nishi et al. 2002c; Wobeser 2002). Reportable disease management for agricultural purposes is typically based on the objective of eradicating the disease from a livestock population (Nishi et al. 2002c). The policy and legislative framework for eradicating reportable diseases in domestic animals is well developed, however, when applied to wildlife, the protocols used by agricultural agencies are usually not compatible with conservation goals (e.g., maintaining genetic diversity, minimal management intervention) (Nishi et al. 2002c). Increasingly, the broader conservation community is examining wildlife disease issues in the context of their impact on the viability of wild populations, conservation translocation programmes, and global biodiversity (Daszak and Cunningham 2000; Deem et al. 2001; Wobeser 2002). Creative disease-ecology research is needed, and an adaptive management framework is required for coping with diseases within a conservation context (Woodruff 1999). An evaluation of the disease management methods presently applied to bison populations is needed and could assist with development of novel conservation-appropriate policies and protocols for managing the health of free-ranging bison populations (Nishi et al. 2002c). Two emerging policy concepts being discussed to manage and control the transmission or distribution of disease at the domestic/wild animal interface include regionalisation and compartmentalisation (CFIA 2002; OIE 2008). Regionalisation offers one means of spatially identifying where disease control measures will occur on the land while compartmentalisation separates the control programmes of wild and domestic animals.


These concepts are being developed and put into practice by state/provincial, federal, and international health agencies to address the complications of managing intractable disease problems in wild animals ranging on large landscapes that also sustain domestic livestock industries and associated local economies (Bengis et al. 2002). National wildlife health strategies have recently been developed in Canada and the U.S. in response to the many difficult disease issues surrounding free-ranging wildlife. The development of national wildlife health programmes paralleled the increasing

profile of wildlife health issues in social and political arenas. These national strategies need to provide clear guidance for coordinated conservation action and a countrywide legislative and policy framework that will influence bison restoration and conservation efforts in North America. It is hopeful that mounting tension between the agriculture, human, and wildlife health communities can be mitigated by developing a comprehensive national wildlife health policy, supportive scientific research programmes, broad stakeholder engagement in decision processes, a conservation-sensitive regulatory framework, and open social discussion about the disease risks from wildlife.


38


Chapter 6

General Biology, Ecology and Demographics Lead Authors: Peter J.P. Gogan, Nicholas C. Larter, James H. Shaw, and John E. Gross Contributors: C. Cormack Gates and Joe Truett

6.1

General Biology

6.1.1.2 Growth

An understanding of the ecology and biology of bison is fundamental to their successful management, conservation, and restoration. Bison have the broadest original range of any indigenous ungulate species in North America, reflecting physiological, morphological, and behavioural adaptations that permit them to thrive in diverse ecosystems that provide their diet of grasses and sedges. Successful population management, conservation of genetic diversity and natural selection, modelling and predicting population level responses to human activities, and managing population structure all depend on understanding the biological characteristics and ecological roles of bison. The purpose of this chapter is to summarise what is currently known about the biology of bison; for an earlier comprehensive review, see Reynolds et al. (2003).

6.1.1 Physiology 6.1.1.1 Metabolism Bison exhibit seasonal variation in energy metabolism. Christopherson et al. (1979) and Rutley and Hudson (2000) observed that metabolisable energy intake and requirements of yearling male bison were markedly lower in winter than summer. This was attributed to a reduction in activity and acclimation. Bison are better adapted to temperature extremes than most breeds of cattle. They expend less energy under extreme cold than do cattle because of the greater insulating capacity of their pelage (Peters and Slen 1964). Cold tolerance of hybrids between bison and cattle is intermediate between the two species (Smoliak and Peters 1955). Tolerance of bison to heat has not been studied, but the original continental range of the species included the dry, hot desert grasslands of northern Mexico, where a small population of plains bison still exists today (List et al. 2007).

Birth weights of intensively managed plains bison have been reported as 25 kg for females and 30 kg for males (Agabriel et al. 1998; Agabriel and Petit 1996; Rutley et al. 1997). Birth weights (near-term foetuses) of free-ranging plains bison range from 14 to 32 kg (McHugh 1958; Meagher 1986; Park 1969). Gogan et al. (2005) estimated that the birth weight of free-ranging bison calves is on average 10% less than that of captive bison. Growth from calfhood to adulthood followed a similar pattern to that of adults, with weight gain during the summer and loss during the winter (P.J. Gogan, unpublished data). Weight gain among calf and yearling plains bison was affected by the influence of the timing and magnitude of summer precipitation on graminoid physical structure (Craine et al. 2009). Differences in weights of plains bison in geographically separate herds have been attributed to differences in climate, nutritional plane, and genetic lineages (Berger and Peacock 1988; Lott and Galland 1987). At Elk Island National Park (EINP), female plains and wood bison achieved asymptotic body weight by six years and maximum body weight at 10 years (Olson 2002; Reynolds et al. 2003). Female plains bison at Wind Cave National Park (WCNP) reached an asymptotic body and maximum body weight at five years (Figure 6.1). Male plains and wood bison at EINP reached an asymptotic body weight at eight to nine years and maximum body weight by 13 years (Reynolds et al. 2003). Male plains bison at WCNP continued to gain weight through the

Figure 6.1 Age-specific live-weights of male and female plains bison at Wind Cave National Park, South Dakota, obtained at fall roundups 1986–1989 and 1991–1999. Data courtesy D. Roddy and B. Meunchau, Wind Cave National Park.


Plate 6.1 Plains bison bull tending a cow, Jackson Valley, Wyoming. Photo: Cormack Gates.

first eight years (Figure 6.1). While differences among populations in body size and weight may be apparent to an observer, comparisons must take in to account the annual cycle of weight gain and loss.

6.1.2

Behaviour

6.1.2.1 Social structure There are many historical observations of huge plains bison herds roaming the Great Plains (Dary 1989; Hornaday 1889; Isenberg 2000; Roe 1970). Observers of both plains and wood bison consistently report a definable herd structure where cows, calves, and immature males form unstable mixed-sex and age groups, and large bulls form separate, smaller groups throughout much of the year (Allen 1876; Berger and Cunningham 1994; Komers et al. 1993; Meagher 1973; Melton et al. 1989; Schuler et al. 2006). Seasonal variations in group sizes are associated with abundance or dispersion of forage (Jarman 1974; Schuler 2006), landscape features (Berger and Cunningham 1994), breeding behaviour (Berger and Cunningham 1994; Meagher 1973; Melton et al. 1989; Komers et al. 1993) and population size (Schuler et al. 2006). The largest aggregations occur during the breeding season when mature bulls join the mixed-sex and age groups. Mean group sizes during the August rut at Badlands National Park range from a mean of 157 in flat terrain to 79 in broken terrain (Berger and Cunningham 1994). Mean maximum group sizes at Yellowstone National Park (YNP) increased from 140 in May to more than 250 in September (Hess 2002). Groups of more than 1,000 bison have been observed during the rut in contemporary Oklahoma (Schuler et al. 2006). Group size rapidly diminishes during autumn in plains bison (Hornaday 1889) to fewer than 30 (Berger and Cunningham 1994; Schuler et al. 2006). Similarly, in wood bison, typical group size is greatest during the pre-rut and rut, then declines during the fall (Komers et al. 1992). Mean maximum group sizes at YNP declined throughout winter from more than 250 in December to 16 in April as the area occupied by bison increased from 1,000 to more than 1,200 km2 (Hess 2002). Male bison form temporary, unstable groups, and exhibit a linear dominance hierarchy, with older, heavier animals dominant over younger smaller males (Komers et al. 1994; Roden et al. 2005). Dominance is also related to age in female bison (Rutberg 1983). Groups of adult or subadult males rarely exceed 10 individuals (Berger and Cunningham 1994). Plains and wood bison population substructure occurs at a broad geographical scale due to traditional use of particular parts of a range by segments of a population (Joly and Messier 40

2001; Olexa and Gogan 2007). Plains bison within the Greater Yellowstone Area show strong fidelity to subpopulations (Christianson et al. 2005; Gogan et al. 2005; Olexa and Gogan 2007) as do wood bison in the Greater Wood Buffalo Ecosystem (GWBE) (Carbyn et al. 1998; 2004; Chen and Morley 2005; Joly and Messier 2004). Bison within subpopulations show stronger cohesion and coordinated movements during summer than in winter (Chen and Morley 2005; Olexa and Gogan 2007). 6.1.2.2 Reproductive behaviour Sexually mature male plains bison join mixed-sex and age aggregations during the rut. Dominant bulls form so-called “tending bonds” with individual cows just prior to, or during, oestrus (Fuller 1960; McHugh 1958; Meagher 1973). The bull will typically attempt to keep other bulls away and to keep the cow near the edge of a mixed-sex and age group until she accepts copulation (Berger and Cunningham 1994; Lott 2002; McHugh 1958). Mature males move away from mixed-sex and age groups at the end of the rut (Berger and Cunningham 1994; Lott 2002). Wood bison also aggregate during the summer (Joly and Messier 2001; Komers et al. 1992). Male wood bison become more solitary with increasing age, are more frequently aggressive, and test females for oestrus more frequently than do younger bulls (Komers et al. 1992). During the rut, mature males join mixed sex and groups to compete for mating opportunities and temporarily leave these groups to recover from high cost breeding activities (Komers et al. 1992). In the experimental absence of mature males during the rut, subadult males fed less and interacted more aggressively than when mature males were present (Komers et al. 1994). 6.1.2.3 Cow-calf behaviour Female plains bison close to parturition have been described as restless and excitable (McHugh 1958). A pregnant cow may


leave the herd prior to calving or give birth within the herd (McHugh 1958). Similarly, for wood bison in the Mackenzie Bison Sanctuary (MBS), females have been observed calving in the midst of herds or in extreme isolation in the forest away from any other animals (N.C. Larter, personal observation). Birthing normally occurs while the female is lying down. The mother typically consumes portions of the afterbirth as she frees the calf from the membranes (Lott 2002; McHugh 1958). The female licks amniotic fluid from the calf’s fur (Lott 2002). Suckling begins shortly after birth and may last as long as 10 minutes (McHugh 1958); although there was a report of a wood bison mother attacking the newborn calf during suckling (Carbyn and Trottier 1987). The close contact between a cow and calf begins to decline after the calf’s first week of life (Green 1992). A calf is typically weaned by seven to eight months of age, although nursing may extend beyond 12 months (Green et al. 1993). The longest associations among bison are between cows and their female offspring; while male offspring may remain with the cow through a second summer, female offspring may remain with the cow through a third summer (Green et al. 1989; Shaw and Carter 1988). The cow may use quick charges or steady advances to defend a calf against threats (Garretson 1938; Hornaday 1889; McHugh 1958). An isolated plains bison cow vigorously defended her calf from a grizzly bear (Ursus arctos), even though the bear was ultimately successful in killing the calf (Varley and Gunther 2002). Similarly, an isolated cow vigorously defended the calf from wolves (Canis lupus) (C. Freese, personal communication). Cows and other members of mixed-sex and age groups may cooperatively protect calves from predators. In response to the approach of a grizzly bear, a mixed-sex and age group of adult plains bison responded by facing the bear in a compact group, with the calves running behind the adults (Gunther 1991). Wolves preferentially attempt to prey upon wood bison mixed-sex and age groups that include calves (Carbyn and Trottier 1987). During wolf attacks, calves moved close to the cow, or to other bison, or to the centre of the bison group (Carbyn and Trottier 1987; 1988), although this defensive response may break down when bison groups move through forested areas that may impede the movements of the calves (Carbyn and Trottier 1988).

rubbing an object, typically a shrub or small tree, with its head, horns, neck, or shoulders (Coppedge and Shaw 1997). Wallowing involves a bison rolling in dry loose ground (or less frequently in wet ground) and tearing at the earth with its horns and hooves as it rolls. Bison prefer to horn aromatic shrubs and saplings (Coppedge and Shaw 1997; Edwards 1978; McHugh 1958; Meagher 1973), which may have insect deterrent properties. Bison have even been observed rubbing on treated telephone posts (Coppedge and Shaw 1997). Soper (1941) observed that horning and rubbing were often associated with harassment by insects. Like wallowing, horning may also constitute aggressive display behaviour. Bison of both sexes and all age classes engage in wallowing behaviour throughout the year (Reynolds et al. 2003), although sexually mature males wallow more frequently during the rut, urinating in the wallow before pawing and rolling (Lott 2002; McHugh 1958). Wallowing by mature males may stimulate oestrus in females (Bowyer et al. 1998), and advertise a male’s physical condition to other males (Lott 2002). Plains bison may also wallow to cool themselves during the hot summer months, or to achieve relief from biting insects (McMillan et al. 2000; Mooring and Samuel 1998). Catlin (in Hornaday 1889) described bison creating wallows in areas with a high water table and rolling in the wallow as it filled with water. The result was pelage matted with mud and clay (Catlin in Hornaday 1889). Coat shedding, rut, and insect harassment occur simultaneously during the summer; therefore in the absence of controlled experimentation, it is not possible to determine the relative influence of these factors on the frequency of horning and wallowing (Coppedge and Shaw 1997). 6.1.2.5 Movements Plains bison frequently travel in single file along well-established trails when moving between foraging patches (Garretson 1938; Hornaday 1889). Historically, plains bison undertook

6.1.2.4 Horning and wallowing All age and sex classes of bison engage in behaviours referred to as horning and wallowing (McHugh 1958). Horning involves an animal

Plate 6.2 Wallowing modifies the landscape. Photos: Dwight Lutesy (inset) and John Gross.


extensive seasonal north-south movements from summer to winter ranges (Seton 1929) on both sides of the Mississippi River (Garretson 1938; Roe 1970) and from the prairies into the Parkland (Campbell et al. 1994). Large herds also remained on the northern prairies throughout winter (Malainey and Sherriff 1996). River valleys were crucial to the survival of bison overwintering on the grasslands (West 1995). Plains bison also undertook seasonal east-west movements from the prairies to the foothills of the Rocky Mountains in winter (Garretson 1938). Inferences from historical reports of seasonal movement patterns are confounded by the timing of the account relative to the impacts of market hunting, establishment of pioneer trails, and construction of the railroads (Roe 1970). In summer, bison on the Great Plains moved to water on an almost daily basis, and on occasion moved from 80 to 160 kilometres over several days to access water (Dary 1989). Plains bison currently occupying the YNP spend summer at higher elevations and move to winter ranges at lower elevations (Aune et al. 1988; Gates et al. 2005; Meagher 1973; Olexa and Gogan 2007). These movements are made over a network of trails, geothermal features, and along the banks of rivers and streams, or along groomed roadways aligned with natural travel routes (Bjornlie and Garrott 2001). Adult males are often the first to pioneer previously unoccupied areas, a behaviour that has been observed in both wood bison and plains bison (Gates et al. 2005). Yellowstone bison have expanded their range in response to increased population densities (Taper et al. 2000) exacerbated by particularly severe winters (Meagher 1989). Wood bison at Wood Buffalo National Park (WBNP) annually travel up to 50 kilometres maximum from a centre of activity (Chen and Morley 2005), and individual wood bison at the MBS range over areas of 179 to 1,442 km2 (Larter and Gates 1990). Wood bison have slowly been expanding their range in the northern boreal forest. Range expansion is generally initiated by large males who then seasonally return from the peripheries of the range to join females and juveniles during the rut (Gates and Larter 1990; N. Larter and J. Nishi unpublished data). Subsequently, mixed-sex and groups move into the expanded peripheral range. Range expansion typically follows periodic high local population densities (Gates and Larter 1990) and is density-driven (Gates et al. 2005).

6.2

Ecology

6.2.1 Plains bison 6.2.1.1 Ecological role Millions of plains bison historically ranged over North America’s grasslands and functioned as a keystone species (Knapp et al. 1999). They shared this landscape with a variety of other large 42

mammals including pronghorn (Antilocapra americana), elk (Cervus elaphus), deer (Odocoileus spp.), wolves, and grizzly bears. At the landscape level, bison served as ecosystem engineers, both responding to, and creating, heterogeneity. An estimated 100 million bison wallows had a major effect on surface hydrology and runoff (Butler 2006). Ephemeral pools of standing water that persisted in wallows for many days following spring snow melt or rainstorms (Knapp et al. 1999) supported a variety of wetland plant species (Collins and Uno 1983; Polley and Wallace 1986). Similarly, bison wallows provided important breeding habitat for the Great Plains toad (Bufo cognatus; Bragg 1940) and the plains spadefoot toad (Spea bombifrons; Corn and Peterson 1996). Bison directly affect vegetation communities through their grazing, physical disturbance, and by stimulating nutrient recycling and seed dispersal (McHugh 1958). Such activities help to maintain meadows and grasslands on which they, and many other animal and plant species, depend. In tallgrass prairie, bison grazing of grasses increased soil temperature, light availability, and soil moisture availability to forb species (Fahnestock and Knapp 1993). The net result was beneficial to forbs not eaten by bison (Damhoureyeh and Hartnett 1997; Fahnestock and Knapp 1993), and may thereby have been beneficial for other herbivores such as pronghorn. Bison grazing of short and mixed-grass prairie vegetation increased the rates of nutrient cycling (Day and Detling 1990), modified plant species composition (Coppock and Detling 1986) and increased the nutritive value of grasses (Coppock et al. 1983a; 1983b; Krueger 1986). Locally, bison consumed forage resources (England and DeVos 1969; Hornaday 1889) and reduced forage height to levels that facilitate colonisation by prairie dogs (Cynomys spp.; Virchow and Hygnstrom 2002). In turn, prairie dog activities enhanced the ratio of plant live: dead material, crude protein content, and digestibility (Coppock et al.1983a; 1983b) and thereby encouraged further grazing by bison over more than 20% of the natural short and mixed grass prairie (Whicker and Detling 1988). While bison grazing was independent of pocket gopher (Geomyidae) activities, it influenced gopher distribution by modifying the distribution and abundance of patches of forbs used by gophers (Steuter et al. 1995). Bison grazing, frequently in conjunction with fire and wallowing, enhanced the grassland heterogeneity necessary to provide suitable nesting sites for a variety of obligate grassland nesting bird species (Knapp et al. 1999). Bison grazing, particularly on recently burned areas, enhances the abundance of breeding bird species, such as upland sandpipers (Bartramia longicauda) and grasshopper sparrows (Ammodramus savannarum), in tallgrass prairie (Fuhlendorf et al. 2009; Powell 2006). Similarly, a number of bird species endemic to the short and mixed grass prairies of North America, such as the mountain plover (Charadrius montanus) and McCown’s Longspur (Calcarius mccownii), were


historically dependent on a combination of bison wallows and prairie dog colonies for nesting sites. These areas were also utilised by ferruginous hawks (Buteo regalis) and long-billed curlew (Numenius americanus) (Knopf 1996). Brown-headed cowbirds (Molothrus ater), also called buffalo birds, occurred in association with bison throughout central North American grasslands prior to the introduction of livestock (Friedman 1929). Cowbirds feed on insects moving in response to foraging bison (Goguen and Mathews 1999; Webster 2005). Grasshopper species richness, composition, and abundance are strongly influenced by interactions between bison grazing and fire frequency (Joern 2005; Jonas and Joern 2007). Bison facilitated dispersal of the seeds of many plant taxa as a result of the seeds becoming temporarily attached to the bison’s hair (Berthoud 1892; Rosas et al. 2008) or via passage through the digestive tract (Gokbulak 2002). Peak passage rate for seeds was 2 days following ingestion (Gokbulak 2002). Horning damage to trees along grassland borders is effective in slowing invasion of trees into shrub and grassland plant communities or in extending the existing grassland into the forest margin. Bison within YNP rubbed and horned lodgepole pine (Pinus contorta) trees around the periphery of open grasslands to the extent that some were completely girdled (Meagher 1973). Similarly horning by wood bison in the MBS has resulted in completely girdled white spruce stands on the periphery of mesic sedge meadows and willow savannas (N.C. Larter, personal observation). Several authors (Campbell et al. 1994; Coppedge and Shaw 1997; Edwards 1978) have suggested that bison, in combination with other factors such as fire and drought, significantly limited the historic distribution of woody vegetation on the Great Plains.

which may differ markedly from pristine conditions (Fahnestock and Detling 2002). Herbivores, including bison, respond to gradients in forage quality and quantity. Hornaday (1889) described a highly nomadic foraging strategy, where plains bison seemed to wander somewhat aimlessly until they located a patch with favourable grazing. A bison herd would then remain and graze until the need for water motivated further movement. This account contrasts with more recent studies of bison foraging, which have found that plains bison actively select more nutritious forages, and forage in a highly efficient manner that satisfies their nutritional needs and compliments diet selection by sympatric herbivores (Coppock et al. 1983a; 1983b; Hudson and Frank 1987; Singer and Norland 1994; Wallace et al. 1995). Spatial variation in forage quality and quantity results from natural gradients in soil moisture, soil nutrients, fire, and other disturbance, as well as from the impacts of foraging by bison. Bison exploit variations in forage quality and quantity at all scales; from selecting small patches of highly nutritious forages on prairie dog towns, to undertaking long-distance migration in response to seasonal snowfall or drought. The following review of bison habitat interactions is based upon North American ecoregions identified by Ricketts et al. (1999) and aggregated by Sanderson et al. (2008).

A decomposing bison carcass initially kills the underlying plants, but subsequently provides a pulse of nutrients, creating a disturbed area of limited competition with abundant resources that enhances plant community heterogeneity (Towne 2000). Carrion from dead bison is an important food resource for both grizzly and black bears (Ursus americana) as well as scavenging birds such as bald eagles (Haliaeetus leucocephalus), ravens (Corvus corax), and black-billed magpies (Pica pica). 6.2.1.2 Contemporary habitat use, nutrition, and foraging The bison is a ruminant with a four-chambered stomach and associations of symbiotic microorganisms that assist digestion of fibrous forage. On lower quality forage, such as grasses and sedges, bison achieve greater digestive efficiencies than domestic cattle, but on high quality forages such as alfalfa, the digestive efficiency of bison and cattle converge (Reynolds et al. 2003). Contemporary studies of plains bison habitat selection in North American grasslands are limited to confined herds artificially maintained at varying densities (Table 6.1)—some of

Plate 6.3 Plains bison bull cratering in snow to forage. Photo: Yellowstone National Park.


Table 6.1 Diets of plains bison at select locations within North American ecoregions.

Plant Type Ecoregion

Northern Mixed Grasslands

Location

Wind Cave NP, SD

Rocky Mountain Forests

Forbs (%)

Woody Plants (%)

Spring

81

7

9

3

Summer

79

9

10

2

Autumn

77

12

6

5

Winter

79

12

2

7

Winter

59

37

4

Reference

Others (%)

Marlow et al. 1984

Westfall et al. 1993

Wydevan and Dahlgren 1985

98

2

Summer

94

5

Lightly grazed

Autumn

99

Winter

94

4

Spring

95

4

Summer

96

4

Autumn

87

2

12

Winter

81

6

11

Spring & Summer

99

Spring

60

39

1

Summer

88

11

1

Autumn

84

16

1

Winter

79

21

1

National Bison Range, MT

Annual

90

1

2

1

McCullough 1980

Yellowstone Northern Range,WY

Winter

53

441

1

1

Singer and Norland 1994

Yellowstone Central Range, WY

Summer

55

37

2 years

>3 years

Wichita Mountains, OK

13

52

67

Wichita Mountains, OK

12

72

Fort Niobrara, NB

Wood bison

Halloran 1968 Shaw and Carter 1989

83

Wolff 1998

62

Van Vuren and Bray 1986

Antelope Island, UT

46

Wolfe et al. 1999

National Bison Range, MT

86

Rutberg 1986

Konza Prairie, KS

66 – 79

Towne 1999

Henry Mountains, UT

Plains bison

Reference

52

Badlands, SD

4

67

Berger and Cunningham 1994

Wind Cave, SD

5

80

Green 1990, Green and Rothstein 1991

Yellowstone – Northern Herd, WY/MT

40

Kirkpatrick et al. 1996

Yellowstone – Central Herd, WY

52

Kirkpatrick et al. 1996

Yellowstone – mixed, WY

73

Pac and Frey 1991

Yellowstone – mixed, WY

79

Meyer and Meagher 1995

Wood Buffalo – Hays Camp, NWT

4

53

Fuller 1962

Wood Buffalo – Lake Claire, AB

12

76

Fuller 1962

Wood Buffalo, NWT and AB

76*

Wood Buffalo, NWT and AB Mackenzie Bison Sanctuary, NWT

Joly and Messier 2004

70** 43 70

Carbyn et al. 1993 Gates and Larter 1990

* no disease ** infected with brucellosis and bovine tuberculosis


by winter severity and the area of wildland fires (Turner et al. 1994; Wallace et al. 2004). Survival of calves to six months is more than 90% in plains bison herds in protected areas, or those that are only lighted hunted in the absence of predators and diseases (Table 6.5). The survival rate for the first six months of life in the presence of wolves at WBNP was 47% (Table 6.5; Bradley and Wilmshurst 2005). At the SRL survival rates for the first six months of life increased from 6% to 30% coincident with a decline in wolf abundance (Table 6.3; Calef 1984). Survival through the first year of life, in the presence of wolves, has been estimated at 10% and 41% for bison at WBNP (Table 6.5; Carbyn et al. 1993; Fuller 1962). Calf survival through the first year of life was 95% for an increasing

herd at the MBS, when wolf abundance was low (Table 6.5; Calef 1984). There are highly variable estimates on survival patterns in the first year of life (Table 6.5). Adult survival rates in disease-free, protected, or lightly hunted, populations of plains bison are more than 95% for sexes combined or females only (Table 6.5). Survival rates for both sexes in increasing populations have averaged 75% for wood bison at the MBS, and 95% for the Jackson plains bison herd (Table 6.5; Larter et al. 2000; USFWS-NPS 2007). At WBNP, bison infected with both brucellosis and BTB experience lower survival rates than do those infected with only one of the two diseases, or not infected at all (Table 6.5; Bradley and Wilmshurst 2005; Joly and Messier 2001; 2004; 2005).

Table 6.5 Age-specific survival rates (%) of plains and wood bison at select locations (mm = male; ff = females).

Age Subspecies

Location and Years Henry Mountains, UT

Plains bison